abdominal muscles: A flat sheet of muscles on the front of the abdomen, between the ribcage and the pelvis.
abdominoplasty: A procedure to remove excess abdominal skin and tighten the underlying stomach muscles. Also known as a tummy tuck.
abduction: Movement of a body part, such as an arm or leg, away from the center of the body.
ablation: A form of treatment that uses electrical energy, heat, cold, alcohol, or other modalities to destroy a small section of damaged tissue.
abrasion: A scraping or rubbing away of the skin or other surface.
abscess: Pus that collects in a pocket of swollen, red tissue. Often occurs on the surface of the skin.
abutment: A tooth or implant to which a fixed prosthesis is anchored.
acceptance-based therapies: Psychotherapy techniques that use mindfulness to help a person recognize and accept thoughts and feelings but not be controlled by them.
accommodation: The eye's ability to focus on objects that are close.
ACE: Abbreviation for angiotensin-converting enzyme, an enzyme that converts the inactive form of the protein angiotensin (angiotensin I) to its active form—angiotensin II.
ACE inhibitor: Abbreviation of angiotensin-converting enzyme inhibitor, a drug used to treat high blood pressure and congestive heart failure.
acetabulum: A curved, bowl-shaped depression in the outer part of the hipbone. The ball-shaped portion at the top of the thighbone fits into this space to form the hip joint.
acetaldehyde: The main breakdown product of alcohol metabolism; accumulation of it in the bloodstream may produce flushing (a feeling of heat in the face or chest) and vomiting.
acetaminophen: A common, over-the-counter drug used to reduce fever and relieve mild to moderate pain, but which does not reduce redness or swelling (inflammation).
acetylcholine: A neurotransmitter (a chemical messenger that sends signals between brain cells) that plays roles in attention, learning, and memory.
Achilles' tendon: A band of connective tissue that connects the calf muscle to the heel bone. This tissue is prone to swelling and/or rupture.
achlorhydria: A condition in which the stomach produces little or no acid. This can affect digestion, cause stomach pain, and keep the body from absorbing vitamins and nutrients.
acne: An inflammatory disease resulting from excess sebum production, follicle plugging, and increased bacterial production.
acquired immunodeficiency syndrome: Usually abbreviated as AIDS. This is the most advanced stage of infection with the human immunodeficiency virus (HIV), which can severely weaken the immune system. People with AIDS get many infections, often from diseases that don't affect people with healthy immune systems.
acquisition: The term given to the brain's absorption of new information to begin creating a memory.
acromioclavicular joint: A shoulder joint that connects the clavicle to the scapula.
actin: One of the proteins that allows cells to move and muscles to contract.
actinic keratosis: Scaly pink or red-brown raised spots or patches on the skin caused by overexposure to the sun. Actinic keratosis may be a precursor to skin cancer.
active surveillance: A strategy for managing early prostate cancer in which a man has regular checkups but does not undergo treatment until the disease shows signs of worsening.
acupressure: Using the thumb or fingers to apply pressure to particular spots, or pressure points, on the body in order to relieve pain.
acupuncture: A treatment based on Chinese medicine. Thin needles are inserted into the skin at specific points on the body. This therapy is used to treat pain and various health problems and to reduce stress.
acute: A condition that comes on suddenly, often with severe, but short-lived symptoms.
acute pain: Severe pain that occurs suddenly and usually lasts a short while.
acute urinary retention: A sudden inability to empty the bladder. Causes include an enlarged prostate gland (in men) or bladder muscle problems.
adaptability: The ability of an organism to change genetically in a way that allows it to deal better with its environmental conditions.
adaptive immunity: The ability of the body to learn to fight specific infections after being exposed to the germs that cause them.
addiction: Loss of control over indulging in a substance or performing an action or behavior, and continued craving for it despite negative consequences.
adduction: Movement of a body part toward or across the midline.
adenocarcinoma: A type of cancer that grows in the layer of tissue known as the epithelium. This tissue lines organs and structures in the body, protecting or enclosing them.
adenoma: A benign growth found in the layer of cells that lines certain organs (epithelial cells).
adenosine triphosphate: An energy-storing molecule that is found in all human cells. Usually abbreviated as ATP.
adequate intake: An estimate of the amount of a nutrient needed by healthy people. The Adequate Intake is used when there isn't enough information to set a recommended dietary allowance (RDA).
adhesion: A band of scar-like tissue that forms between two surfaces inside the body, connecting tissues or organs which are not normally connected.
adipose tissue: Fat-filled tissue.
adjuvant therapy: Extra therapy given after a primary treatment, to increase the effectiveness of the primary treatment. For example, using chemotherapy after surgery or radiation treatment for cancer.
adrenal glands: Glands that sit on top of each kidney and secrete stress hormones.
adrenaline: Stress hormone that puts the body on high alert. Changes include faster heartbeat, more rapid breathing, greater energy, and higher blood pressure. Also called epinephrine.
adult day services: Centers providing daytime services to adults who need supervision, social support, or assistance with daily activities.
adulterant: An ingredient in a medicinal product (herb, supplement, or prescription drug), which dilutes the purity of the product and does not contribute to its therapeutic effects.
advance care directive (or advance medical directive): A legal document that describes the kind of medical care a person want if an accident or illness leaves him or her unable to make or communicate decisions.
advanced sleep phase syndrome: A pattern of falling asleep and waking up earlier than wanted that worsens progressively over time.
aerobic: Any process that requires oxygen. Often used to describe a form of exercise, aerobic exercise.
aerobic exercise: Physical activity that speeds breathing, improves heart and lung function, and offers many other health benefits. Examples include brisk walking, running, or cycling.
aerophagia: Excessive swallowing of air.
aesthetician: Licensed skin care professional who performs procedures such as deep cleansing, low-grade chemical peels, microdermabrasion, and postsurgical skin care.
after-cataract: Clouding of the lens of the eye that can occur months or years after cataract surgery.
age-related cognitive decline: The slight loss of memory and slowing of the brain's information processing that occurs with normal aging.
age-related macular degeneration: A potentially blinding condition that destroys sharp central vision.
agnosia: A rare disease in which a person can't recognize objects, shapes, or people. Often due to a brain or neurological condition.
agonist: 1) A substance that triggers a physiological response when it combines with a receptor. 2) A muscle whose contraction is opposed by another muscle.
agoraphobia: Fear and avoidance of public places and open spaces.
AIDS: abbreviation for acquired immunodeficiency syndrome, the most advanced stage of infection with the human immunodeficiency virus (HIV).
AIDS dementia: A loss of brain function that occurs rapidly in some AIDS patients; marked by forgetfulness, difficulty thinking, and trouble focusing.
albinism: A group of inherited conditions that typically appear as a reduction or absence of melanin pigments in the skin, hair, and eyes.
albumin: A protein made by the liver. Abnormal levels of this substance may indicate liver or kidney disease.
albuminuria: High amounts of albumin (a protein made by the liver) in the urine, possibly indicating kidney dysfunction.
alcohol abuse: Continuing consumption of alcohol despite alcohol-related social or interpersonal problems.
alcohol dehydrogenase: A liver enzyme that metabolizes alcohol into a substance called acetaldehyde, which is toxic. Sometimes referred to as ADH.
alcohol dependence: A chronic, progressive disease characterized by excessive and often compulsive drinking, impaired control over drinking, use of alcohol despite adverse consequences, and withdrawal symptoms when alcohol use is discontinued. Also known as alcoholism.
alcoholism: Another term for alcohol dependence: A chronic, progressive disease characterized by excessive and often compulsive drinking, impaired control over drinking, use of alcohol despite adverse consequences, and withdrawal symptoms when alcohol use is discontinued. Also known as alcoholism.
aldosterone: A hormone secreted by the adrenal glands that helps regulate blood pressure by controlling sodium and potassium levels in the body.
alendronate: A drug used to treat and prevent osteoporosis by slowing bone loss.
alimentary canal: Another term for the gastrointestinal, or digestive, tract.
allele: One of two or more versions of a gene. Different alleles produce variations in inherited characteristics, such as eye color.
allergen: A substance such as fur, pollen, or dust that produces an allergic reaction.
allergic: Having a sensitivity to one or more normally harmless substances.
allergic rhinitis: A seasonal or year-round allergic condition marked by sneezing, runny nose, and congestion. The most common type of allergy, it is caused by an IgE-mediated immune response to inhaled airborne allergens.
allergy: An immune system reaction (for example, rash, fever, sneezing, or headaches) to something that is normally harmless.
allodynia: Pain resulting from something not normally painful, such as a light touch.
alopecia areata: An autoimmune condition that appears as patchy hair loss on the scalp that may result in permanent hair loss.
alopecia totalis: Hair loss that involves the entire scalp.
alopecia universalis: Hair loss that involves the entire body.
alpha blockers: A group of drugs that lower blood pressure by blocking the effects of adrenaline or adrenaline-like substances on cells' alpha receptors. Also used to treat some prostate gland problems. Alpha blockers are also known as alpha-adrenergic antagonists, alpha-adrenergic blocking agents, and alpha-adrenergic blockers.
alpha cells: Cells in the pancreas that produce the hormone glucagon.
alpha hydroxy acids: Fruit-derived acids used in creams and lotions to act as exfoliants.
alpha waves: A type of brain wave generated when a person is relaxed, awake, and receiving no visual input (eyes closed or in the dark).
alpha-delta sleep: Abnormal deep sleep; also called non-restorative sleep.
alpha-glucosidase inhibitor: A drug used to treat Type 2 diabetes.
alveolar bone: The part of the jawbone that supports the teeth.
alveoli: Tiny air sacs in the lung. They are where oxygen enters and carbon dioxide leaves the bloodstream.
Alzheimer's disease: A progressive brain disease that causes memory loss, impaired thinking, and personality changes.
ambulatory: Able to walk; not confined to a bed.
AMD: Abbreviation for age-related macular degeneration, a potentially blinding condition that destroys sharp central vision.
amnesia: Unusual memory loss or forgetfulness.
amputation: The surgical removal of a limb or other body part.
Amsler grid: A tool used to check for vision problems, particularly macular degeneration. The grid looks like graph paper with a dot in the center.
amygdala: Part of the brain involved in memory and emotion.
amylase: An enzyme secreted by the pancreas that breaks starch into sugar.
amyloid: A protein that collects in tissues when certain diseases, including Alzheimer's disease, are present.
anaerobic: Any process that doesn't require oxygen. Often refers to a form of short, high intensity exercise, known as anaerobic exercise.
anaerobic exercise: Exercise that improves the efficiency of energy-producing systems that do not rely on oxygen. Examples include sprinting and weight lifting.
anagen: The active growth phase of the hair-growth cycle.
anal canal: The last inch of the large intestine, leading to the anal opening.
analgesia: Absence of pain.
analgesic: A drug or other substance such as aspirin, acetaminophen, or morphine that is used to relieve pain.
analytic variability: Differences in how a test is done, for example how a sample is prepared, which can affect test outcomes.
anaphylaxis: A severe allergic reaction, causing symptoms spanning from itching and swelling to trouble breathing, convulsions, shock, and coma.
androgen: Any of a group of male sex hormones, including testosterone, that controls male characteristics such as beard growth.
androgenetic alopecia: Female- and male-pattern baldness. The condition appears to involve a heightened response by the hair follicle to androgen levels in the body.
androgen-independent prostate cancer: Prostate cancer that no longer responds to hormone therapy.
anemia: Having a lower than normal amount of red blood cells or hemoglobin (an oxygen-carrying protein inside red blood cells), leading to low energy, weakness, and other symptoms.
anencephaly: A birth defect in which an infant is born without most of the brain or without the skull bones covering the brain.
anesthesia: Temporarily blocking sensation, especially the feeling of pain.
aneurysm: A bulge or swelling on a portion of a blood vessel, due to weakness in the wall of that vessel.
angina pectoris: Temporary chest pain that occurs when the heart isn't getting enough oxygen and blood, usually occurring in response to physical activity or stress.
angiogenesis: The formation of new blood vessels.
angiography: A test that shows how blood moves through the blood vessels and heart. It uses x-rays and the injection of a fluid called a contrast agent that can be seen on the x-rays.
angioplasty: A procedure used to open blocked or narrowed arteries, most commonly by inserting a thin tube, or catheter, into the affected artery and inflating a balloon.
angiotensin: A protein that raises blood pressure by narrowing blood vessels and causing the kidneys to store more sodium and water.
angiotensin I: An inactive form of the protein angiotensin. It is the precursor to the active form, angiotensin II.
angiotensin II: The active form of the protein angiotensin, which raises blood pressure by narrowing blood vessels and causing the kidneys to store more sodium and water.
angiotensin II receptor blockers: A class of drugs that blocks the effects of angiotensin. Like ACE inhibitors, they keep coronary arteries open, lower blood pressure, and reduce the heart's workload.
angiotensin-converting enzyme: An enzyme that converts the inactive form of the protein angiotensin (angiotensin I) to its active form—angiotensin II. Usually abbreviated as ACE.
angiotensin-converting enzyme inhibitor: A drug used to treat high blood pressure and congestive heart failure. These drugs stop the production of angiotensin II. This lowers blood pressure and reduces the heart's workload. Usually abbreviated as ACE inhibitor.
ankle-brachial index: A test that compares blood pressure at the ankle with blood pressure at the elbow. A difference between the two indicates the presence of peripheral artery disease.
ankylo-: Means crooked or bent; refers to stiffening of a joint.
ankylosing spondylitis: A disease that leads to swelling between the disks of the spine and in the joints where the pelvis and spine meet. Causes back pain and stiffness and can limit movement.
annulus: Term used to describe ring or circle shaped objects or body parts.
annulus fibrosus: The tough outer covering of the discs in the spine.
anorectal dysfunction: Abnormal functioning of the anus and rectum, causing constipation or the inability to control bowel movements.
anorexia: An eating disorder in which a person has an intense fear of gaining weight and severely limits calories to the point of near starvation.
antagonist: The muscle opposing the major muscle required to do a task. It works to help balance movement and ward off injury.
anterior myocardial infarction: A heart attack affecting the front of the heart.
antiandrogen: A drug that blocks or interferes with the activity of male sex hormones.
antibiotic: A substance that kills or slows the growth of bacteria.
antibody: A protein made by the immune system to protect the body from harmful substances, called antigens.
anticoagulant: A substance that helps prevent blood from clotting.
anticoagulants: Drugs that diminish the blood's ability to clot. Anticoagulants are sometimes called blood thinners even though they do not thin the blood. Commonly used anticoagulant drugs include heparin and warfarin.
anticonvulsants: Drugs used to treat seizures.
anti-cyclic citrullinated peptide: An antibody used to help diagnose rheumatoid arthritis.
antidepressant: A psychiatric drug used to treat mood disorders, such as depression.
antiemetic: A drug that prevents nausea and vomiting.
antigen: Any substance that the body sees as harmful or foreign, causing the immune system to form antibodies in defense.
antigen-presenting cell: Specialized white blood cells that detect harmful substances in the body and then signal other immune system defenders (known as T-cells) to mount a defense.
antihistamine: Medications that treat allergies and reduce symptoms such as sneezing and itching by blocking histamine, the substance in the body which causes these symptoms.
antihypertensives: Medications used to lower and control high blood pressure.
antileukotriene: A type of asthma medication that reduces swelling in airways and prevents muscles near the airways from tightening.
antimicrobial: A general term for antibiotics and other drugs that fight microscopic organisms in the body, such as bacteria, viruses, fungi, and parasites.
antioxidant: Substances that protect the body from molecules that damage cells (free radicals); examples include beta carotene, vitamin C, vitamin A, and vitamin E.
antiplatelet agents: Medications or other substances that prevent blood cells called platelets from clustering and forming blood clots.
antipsychotic: A drug used to treat schizophrenia and other severe mental health disorders; relieves symptoms such as delusions and hallucinations.
antiseptic: Substances used on wounds to prevent or treat infection; they kill or slow the growth of disease-causing organisms, such as bacteria, on the surface of the body.
antispasmodic drugs: Drug that relieves cramps and muscle spasms.
antithyroid drugs: Drugs used to treat an overactive thyroid.
anus: The external opening at the end of digestive tract where feces are expelled.
aorta: The large artery emerging from the heart's left ventricle that distributes blood to the body.
aortic valve: A valve on the left side of the heart that acts as a one-way gate, opening to allow blood to leave the left ventricle and closing to prevent blood from leaking back into that ventricle.
aphasia: Difficulty speaking or comprehending language; a common occurrence after a stroke affecting the left hemisphere of the brain, where language is processed.
apnea: A temporary pause in breathing during sleep that can be very brief or can last so long that the amount of oxygen in the blood drops dangerously low.
apolipoproteins: Proteins that combine with cholesterol and triglyceride to form lipoproteins.
apoptosis: A process of programmed cell death in which redundant or flawed cells destroy themselves.
amyloid precursor protein: A normal brain protein that under certain circumstances produces beta amyloid, abnormal protein deposited in the brain in Alzheimer's disease. Usually abbreviated as APP.
apraxia: A brain disorder in which a person cannot perform certain actions, such as combing hair, picking up a pencil, or speaking, even though they want to and have the physical ability to do so.
aqueous humor: Clear fluid that fills the front part of the eye.
ARB: Abbreviation for angiotensin II receptor blockers, a class of drugs that blocks the effects of angiotensin. Like ACE inhibitors, they keep coronary arteries open, lower blood pressure, and reduce the heart's workload.
arbovirus: A virus transmitted by mosquitoes or other member of the arthropod phylum.
arousal: The state of being awake or reactive to stimuli through one or more of the five senses.
arrector pili: The small muscle associated with an individual hair follicle that enables hair to stand on end.
arrhythmia: An abnormal heart rhythm caused by a disturbance in the heart's electrical system.
arterial resistance: The pressure that the artery walls exert on blood flow; in general, the less elastic the arteries, the greater the arterial resistance and the higher the blood pressure.
arteriography: A test that uses x-rays and a special dye to see inside arteries.
arterioles: Small, muscular branches of arteries.
arteriosclerosis: A term encompassing a variety of conditions in which artery walls thicken and become less flexible. Sometimes called hardening of the arteries. Arteriosclerosis occurs when cholesterol-rich plaque forms on the inner lining of arteries (atherosclerosis), when artery walls become calcified, or when high blood pressure thickens the muscular wall of arteries.
arteriovenous malformation: Abnormal connections between veins and arteries, usually caused by a birth defect.
artery: A blood vessel that carries blood away from the heart and to various parts of the body.
arthr-: A prefix meaning "joint.''
arthritis: A condition in which joints are inflamed, causing pain, stiffness, swelling, and sometimes loss of movement.
arthrocentesis: A procedure to drain fluid from a joint using a syringe.
arthrodesis: Joining together two bones to reduce pain and provide stability to a damaged, arthritic, or painful joint.
arthropathy: Joint disease or disorder.
arthroplasty: Surgically rebuilding or replacing a joint, usually to relieve arthritis or fix an abnormality.
arthroscopy: A procedure where a surgeon makes a small cut in the skin and inserts tiny lenses, lighting, and other instruments to diagnose or repair joint problems.
articular cartilage: Smooth white tissue that covers the ends of bones where they come together to form joints.
articular processes: Bony projections on vertebra.
asphyxia: A life-threatening lack of oxygen due to drowning, choking, or an obstruction of the airways.
aspiration: Breathing in a foreign object. Also, the process of suctioning fluid, tissue, or other substances from the body.
aspirin: A drug that relieves pain, fever, and swelling, and inhibits the formation of blood clots.
assisted living: Live-in facilities for adults who need help with certain things, but do not need round-the-clock care. They provide residents with supervision and certain services, such as meals, transportation, or help with dressing, grooming, and other daily activities.
association cortex: The part of the cerebral cortex involved in processing information, rather than movement or sensory experiences.
asthma: A disease that inflames and narrows airways, causing wheezing, shortness of breath, coughing, and tightness in the chest.
astigmatism: Blurry vision caused by an irregular curve in the cornea of the eye.
astringent: A substance that contracts skin tissues and shrinks pores.
asymptomatic: Showing no signs or symptoms of disease, whether or not disease is present.
asystole: The absence of electrical activity in the heart.
ataxia: Being unable to control movement; symptoms include shaking and an unsteady walk.
atheroma: An abnormal build-up of fatty plaque inside an artery.
atherosclerosis: The buildup of fatty deposits (plaque) in the walls of arteries, causing narrowing and reduced blood flow; the disease responsible for most heart attacks and many strokes.
atherosclerotic plaque: A mixture of fats, cholesterol, and other tissue that builds up on artery walls.
atherothrombotic stroke: A type of stroke that occurs when a large artery to the brain is completely blocked by the formation of a clot.
athlete's foot: A foot infection caused by fungus; symptoms include cracking and peeling skin and itchiness. Also known as tinea pedis.
atlas: Another name for the topmost vertebra of the neck, which lies just beneath the skull. Also called C-1.
atopic: Having an inherited predisposition to allergies.
atopic dermatitis: A long-term skin condition, most common in babies and children, in which areas of the skin are dry, itchy, red, and may crack. Also known as eczema.
atopic rhinitis: A seasonal or year-round allergy marked by sneezing, runny nose, and congestion.
atopy: The inherited tendency to develop allergies.
ATP: Abbreviation for adenosine triphosphate, an energy-storing molecule that is found in all human cells.
atria: The upper chambers of the heart. There are two of these—the right atrium and the left atrium.
atrial fibrillation: A disorder in which the two upper chambers of the heart beat fast and erratically. Because blood isn't pumped out of these chambers fully, it may pool and form clots that could lead to a stroke.
atrioventricular node: Also known as the AV node. A major part of the electrical system in the heart that acts as a gateway between the atria and the ventricles. An electrical signal generated by the sinoatrial node (the heart's natural pacemaker) moves through the heart until it reaches the atrioventricular node, a cluster of cells at the bottom of the right atrium. The AV node delays the signal before it is passed to the ventricles. This lets the atria fully contract before the ventricles contract.
atrium: One of the two upper chambers of the heart.
atrium: One of the heart's two upper chambers (the plural form is atria). The right atrium receives deoxygenated blood from the body; the left atrium receives oxygenated blood from the lungs.
atrophy: Wasting away of an organ or tissue due to undernourishment, disease, or aging.
atypical lobular hyperplasia: An overgrowth of abnormally shaped cells in areas of the breast that produce milk (lobules). atypical lobular hyperplasia is not cancerous but may become cancer.
audiogram: A chart that shows a person's ability to hear at different pitches or frequencies.
audiologist: A health professional who assesses hearing and fits hearing aids.
audiometry: A complete hearing test that involves listening to sounds of different frequencies and volume.
auditory nerve: A nerve in the inner ear that transmits information about sound to the brain.
aura: Sensations such as chills, flashes of light, or a blind spot that come just before the occurrence of medical problems such as migraines or seizures.
autoantibodies: Proteins created by the immune system that mistakenly target healthy cells, tissues, or organs.
autoimmune disease: A disease in which the immune system mistakenly identifies healthy tissues and organs as threats and responds by attacking and destroying them.
autoimmune response: When the body's immune system mistakenly views the body's own tissues and organs as foreign invaders and attacks them.
autologous fat transplant: Removal of fat from one part of the body to use as filler in another part, for example, to fill wrinkles and lines in the face and lips.
autonomic nervous system: The part of the nervous system that controls involuntary actions, such as blood pressure or breathing. It also plays an important role in the fight or flight response to danger.
autonomic neuropathy: Damage to the nerves that control involuntary body functions, such as digestion, heart rate, and bladder and bowel function.
autopsy: Surgically opening and examining a body after death to see if any diseases are present and to determine the cause of death.
AV node: Abbreviation for atrioventricular node, a major part of the electrical system in the heart that acts as a gateway between the atria and the ventricles. An electrical signal generated by the sinoatrial node (the heart's natural pacemaker) moves through the heart until it reaches the atrioventricular node, a cluster of cells at the bottom of the right atrium. The AV node delays the signal before it is passed to the ventricles. This lets the atria fully contract before the ventricles contract.
avulsion: The tearing away of one part of the body from another—for example, a tendon tearing away from a bone.
axillary: The armpit.
axis: The second vertebra of the neck (from the skull); also called the C-2 vertebra.
axon: The long, slender extension of a nerve cell that conducts electrical impulses away from the nerve's cell body and on to nearby nerves.
axon terminal: The end of an axon.
B cell: White blood cells that come from bone marrow, and produce antibodies to fight off disease.
bacteria: Tiny single-celled organisms. Some bacteria cause disease, although most are harmless.
balance: Ability to maintain equilibrium while stationary or moving.
balloon angioplasty: A procedure to open clogged heart arteries. A surgeon inserts and inflates a tiny balloon. It widens the blocked artery then expands a small wire mesh tube to keep the artery open.
balloon dilation: A surgical procedure to open a narrowed vessel or tube, such as the urethra, esophagus, or artery. A small, deflated balloon is inserted into the area and inflated to widen it.
bariatric surgery: One of several types of weight loss surgery performed on people who are dangerously overweight, to restrict or reduce food intake and/or absorption.
barium study: An imaging test that allows doctors to see the inside of the esophagus and upper stomach. It involves swallowing a barium solution, which coats the esophagus and makes it possible for x-rays to see the inside of the intestine.
Barrett's esophagus: The abnormal growth of stomach or small intestine cells in the esophagus, resulting from damage caused by the reflux of stomach acid; occasionally may transform into cancer.
basal cell carcinoma: The most common skin cancer. Basal cell carcinoma doesn't spread to internal organs.
basal ganglia: Clusters of nerve cells deep in the brain that play an important role in movement.
baseline EKG: An electrocardiogram (EKG) tracing taken in a healthy individual for later comparison to subsequent EKGs.
basilar artery: The artery that supplies blood to the cerebellum, the brainstem, and the back of the brain.
benign: Harmless; often used to refer to a tumor that is not cancerous and does not usually spread.
benign orgasmic headache: A severe headache that occurs when orgasm is reached.
benign prostatic hyperplasia: A noncancerous enlargement of the prostate gland that obstructs the flow of urine. Often called BPH.
benzodiazepines: Anti-anxiety medications that work by helping to maintain levels of the neurotransmitter gamma-aminobutyric acid (GABA) in the brain.
bereavement: The period of grief and mourning after a death.
beriberi: A nervous system or heart disorder caused by lack of the vitamin thiamine (B1).
Bernstein test: A test to try to reproduce heartburn symptoms; used by doctors to diagnose GERD (gastroesophageal reflux disease).
beta blockers: Medications that block epinephrine (adrenaline) and norepinephrine from attaching to certain parts of nerve cells known as beta receptors. Used to treat high blood pressure, heart rhythm problems, migraines, panic attacks, and other conditions.
beta carotene: A richly colored compound (red, yellow, or orange) found in many plants, fruits, and vegetables that the body can convert into vitamin A.
beta cells: Cells that make and secrete insulin; located in the islets of Langerhans of the pancreas.
beta agonists: A medication that opens airways by relaxing the muscles around the airway; used to treat asthma or COPD (chronic obstructive pulmonary disease).
beta amyloid: An abnormal protein deposited in the brain in Alzheimer's disease.
beta blockers: A class of drugs that slow the heartbeat, lessen the force of each contraction, and reduce the contraction of blood vessels in the heart, brain, and throughout the body by blocking the action of beta-adrenergic substances such as adrenaline (epinephrine) at the beta receptor. Beta blockers, also known as beta adrenergic blocking agents, are used to treat many cardiovascular conditions, including abnormal heart rhythms, angina, and high blood pressure. They also improve survival after a heart attack.
biguanides: Medications that stop the liver from making excess glucose (sugar) and improve sensitivity to insulin.
bile: A thick, yellow-green fluid produced by the liver that aids in digestion.
bile acids: Fatty substances made by the gallbladder that aid in digestion.
bilevel positive airway pressure: A machine that helps people get more air into their lungs when sleeping by increasing the pressure or force of air when breathing in; often used to treat sleep apnea.
binge drinking: Heavy bouts of drinking interspersed with periods of abstinence; often refers to the consumption of five or more alcoholic beverages within one day.
binocular vision: The ability of both eyes to focus on an object and form a single visual image.
Binswanger's dementia: A type of dementia caused when blood flow is interrupted to the white matter of the brain, which lies beneath the cerebral cortex.
bioavailability: How quickly and completely the body can absorb and use a nutrient.
biochanin A: A natural compound found in soybeans that may help prevent cancer from spreading. It is a type of flavonoid.
biochemical recurrence: Usually used regarding prostate cancer. It refers to a post-treatment increase in the level of prostate-specific antigen in the bloodstream, indicating that prostate cancer has recurred or spread following the original treatment. Also called biochemical failure.
biofeedback: An treatment that helps people learn to gain control over normally unconscious body functions, such as breathing and heart rates.
biological variability: Normal fluctuations over time in the levels of a substance being measured (such as cholesterol).
biomarker: A distinctive biological indicator of an event, process, or condition.
biopsy: The removal of a small piece of tissue from the body for examination under a microscope.
bisphosphonate: Medications, including alendronate and etidronate, used to prevent and treat osteoporosis by slowing the breakdown of bone.
blackout: An episode of temporary memory loss resulting from the ingestion of alcohol or other drugs.
bladder neck: Where the bladder and urethra meet.
blepharoplasty: Cosmetic surgery to improve the appearance of droopy eyelids by removing excess skin and fat.
blister: A small pocket of fluid that develops between the upper layers of skin; often caused by friction or burns.
blocking agent: Substance that prevents a biological activity or process.
blood alcohol concentration: A measure of the amount of alcohol in the blood.
blood clot: A coagulated mass that occurs when blood cells stick together and form a solid.
blood pressure: The force blood exerts against the walls of the arteries. Optimal blood pressure is less than 120/80 mm Hg.
blood urea nitrogen test: A test that measures levels of urea in the blood to assess how well the kidneys are functioning.
blood vessels: Hollow tubes that transport blood throughout the body; includes arteries, veins, and capillaries.
BMD: Abbreviation for bone mineral density, the amount of mineralized bone tissue in a given area.
BMI: Abbreviation for body-mass index, a measure of body fat estimated from a person's height and weight. A healthy BMI is defined as 18.5 to 24.9. BMI = weight (in kilograms) divided by height (in meters) squared. Using English units, multiply weight in pounds by 703, then divide the result by height in inches, and divide that result by height in inches.
body mass index: A measure of body fat estimated from a person's height and weight. A healthy BMI is defined as 18.5 to 24.9. BMI = weight (in kilograms) divided by height (in meters) squared. Using English units, multiply weight in pounds by 703, then divide the result by height in inches, and divide that result by height in inches.
bolus: A soft mass of chewed food. Alternatively, a single large dose of a medication given intravenously.
bone mass: The total amount of bone tissue in the body.
bone mineral density: The amount of mineralized bone tissue in a given area.
bone scan: A test in which radioactive material is injected into a person's bloodstream to help produce images of bones; often used to detect cancer or bone diseases.
borborygmi: Stomach growling; the rumbling noises caused by gas moving through the intestine.
Botox: Brand name for a drug made of botulinum toxin type A that is injected into muscles and weakens them to ease the appearance of wrinkles.
Bouchard's nodes: Hard, bony growths that form on the middle joints of fingers in people with osteoarthritis.
bowel: The small or large intestine.
BPH: Abbreviation for benign prostatic hyperplasia, a noncancerous enlargement of the prostate gland that obstructs the flow of urine.
brachial plexus: A network of nerves that are rooted at the cervical spine and provide sensation and movement to the shoulder and arm.
brachytherapy: Treatment in which a surgeon implants seeds or pellets of radioactive material in the body to destroy cancer cells.
bradycardia: A slow heart rate, usually below 60 beats per minute.
brain imaging: Technologies that allow doctors to view the structure of the brain or see how different parts of the brain function; examples include computed tomography (CT), magnetic resonance imaging (MRI), functional MRI (fMRI), and positron emission tomography (PET).
brain stem: The part of the brain that connects the brain with the spinal cord and controls movement, sensation, and reflexes.
brain waves: Electrical impulses generated by the firing of nerve cells in the brain (neurons).
breast augmentation: Cosmetic surgery to increase the size of the breasts.
breath focus: A form of meditation aimed at bringing on a state of relaxation.
Broca's area: The part of the brain (in the frontal lobe of the left hemisphere) responsible for language comprehension and speech.
bronchial tubes: The airways that connect the lungs to the trachea (windpipe) and allow air to pass into and out of the lungs.
bronchiole: A small airway in the respiratory system that connects to the alveoli (air sacs); a branch of the bronchial tubes.
bronchodilator: Medication that eases breathing by relaxing the muscles surrounding the bronchial tubes.
bruit: Unusual sound, heard through a stethoscope, that blood makes when it rushes past an obstruction, like a blockage in an artery.
bunion: A bump of bone or tissue that forms at the big toe joint, causing inflammation and considerable pain.
bunionette: A small, painful bony bump that forms on the outside of the foot, at the base of the small toe.
bursa: A protective, fluid-filled sac located in or near the joints that cushions the movement of bone against tendons, skin, and muscle.
bursitis: Pain and swelling of the bursa, the small fluid filled pads that act as cushions in or near the joints.
bypass: A procedure used to divert the flow of blood or other fluids. When referring to the heart, shorthand for coronary artery bypass surgery, used to divert blood flow around a blocked coronary artery.
CABG: Abbreviation for coronary artery bypass graft. Surgery to improve blood flow to the heart by diverting blood around a blocked artery.
calcification: The buildup of calcium deposits in soft tissue, causing it to harden. Often seen in breast tissue by mammography or in coronary arteries by x-ray or cardiac CT scans.
calcitonin: A hormone that can stimulate bone growth and is sometimes used to treat osteoporosis.
calcium: A mineral that the body needs for many vital functions, including bone formation, regulation of heart rate and blood pressure, and muscle contraction.
calcium channel blockers: A class of drugs that lowers blood pressure, slows the heart rate, and decreases the heart's need for oxygen by blocking the movement of calcium into the heart and the muscle cells surrounding blood vessels.
callus: Hardened, thick skin that forms after repeated friction; often found on hands and the bottom of feet.
calorie: The unit for measuring the amount of energy in food.
cancellous bone: One of two types of tissue that form bone; this type is commonly found at the center of long bones and makes up a large part of the hip and spine. Also known as trabecular bone.
cancer: A group of diseases in which abnormal cells grow in an uncontrolled way, sometimes forming tumors.
capillaries: The body's smallest blood vessels; they deliver oxygen and nutrients to tissues.
capsaicin: An chemical found in hot chili peppers that is used in some pain relief creams.
carbohydrate: The sugars and starches in food that provide the body with most of its fuel. Carbohydrates are one of three primary nutrients along with fats and proteins.
carbohydrate counting: Keeping track of the grams of carbohydrates eaten in order to control weight.
carbon monoxide: An odorless, colorless gas that is toxic to humans and animals at high levels; it is produced by cars, furnaces, fireplaces, and other equipment powered by combustion.
carcinogen: Any substance that can cause cancer.
carcinogenesis: The process by which a normal cell becomes cancerous.
carcinoma: A cancerous tumor that develops in the tissue that lines the organs of the body (the epithelium).
cardiac: Pertaining to the heart.
cardiac arrest: The sudden cessation of contractions capable of circulating blood to the body and brain. Also called sudden cardiac arrest. Cardiac arrest usually occurs as a result of a rapid ventricular rhythm (ventricular tachycardia) or a chaotic one (ventricular fibrillation). Death occurs within minutes unless cardiopulmonary resuscitation and defibrillation are available.
cardiac catheterization: A procedure to diagnose or treat heart problems; a long, thin, flexible tube is inserted into a blood vessel in the arm, neck, or upper thigh and maneuvered into the heart to evaluate various heart functions.
cardiac myocytes: Heart-muscle cells.
cardiac output: The amount of blood the heart is able to pump into circulation; specifically measured as the amount of blood the left side of the heart can pump in one minute.
cardiac resynchronization therapy: A pacemaker-based therapy for heart failure that improves the heart's pumping efficiency by coordinating (resynchronizing) the beat of the ventricles.
cardiac tamponade: When fluid or blood pools within the sac surrounding the heart, squeezing the heart and interfering with its ability to pump.
cardioplegia: Temporarily stopping the heart during heart surgery.
cardiopulmonary: Pertaining to the heart and lungs.
cardiopulmonary bypass: The use of a machine (heart/lung machine) to circulate and oxygenate the blood while surgery is performed on the heart.
cardiopulmonary bypass machine: A pump used to oxygenate and circulate blood through the body while the heart is stopped during open-heart surgery.
cardiopulmonary resuscitation: A combination of chest compressions and mouth-to-mouth breathing that keep oxygenated blood circulating to the brain and tissues. Commonly known as CPR.
cardiorespiratory endurance: A component of physical fitness that relates to the ability of the circulatory and respiratory systems to supply oxygen during sustained physical activity. Also known as cardiorespiratory fitness.
cardiovascular: Pertaining to the heart and blood vessels.
cardioversion: The use of an electrical shock to stop an abnormal heart rhythm (an arrhythmia) and restore a normal one (sinus rhythm). Cardioversion can be external, using pads applied to the chest, or internal, from a pacemaker-like device called an implantable cardioverter defibrillator (ICD).
carminative: An herb said to expel gas from the digestive system, easing stomach discomfort.
carotenoids: Compounds such as lycopene and beta carotene that give red, yellow, and orange color to certain plants.
carotid artery: One of two major blood vessels found on either side of the neck. The carotid arteries supply blood to the brain.
carotid artery disease: Narrowing of the carotid artery by the buildup of plaque. Sometimes called carotid artery stenosis. It is a major risk factor for ischemic stroke.
carotid bruit: An abnormal sound heard with a stethoscope in the carotid artery; people who have carotid bruits have a greater risk of having a stroke.
carotid duplex Doppler scanning: An ultrasound image of the carotid arteries.
carotid endarterectomy: Surgery to remove fatty plaque buildup from the carotid artery and restore blood flow to the brain.
carpal tunnel syndrome: A condition that occurs when the median nerve, which runs from the forearm through the hand, is compressed; symptoms include pain, tingling, and numbness, as well as hand weakness.
cartilage: Stiff connective tissue that provides support to other tissues and cushions joints.
cartilaginous joint: A joint in which the bones are firmly connected by cartilage, so that only slight movement is possible.
case-control study: A research study that compares one group of people with a particular disease to a very similar group that does not have the same disease.
catagen: The transition phase of the hair-growth cycle.
cataplexy: Sudden paralysis of some or all muscles brought on by laughter, anger, fright, or strong emotions; a hallmark of narcolepsy.
cataract: A clouding or fogging of the lens of the eye that may blur or tint vision.
catastrophic reaction: A strong emotional reaction to a minor event.
cathartic: An agent with a strong laxative effect.
catheter: A thin tube that is inserted into the body to provide or drain fluids, or to carry tiny surgical instruments and cameras in minimally invasive surgeries.
cation: A positively charged ion; cations in the body include sodium, potassium, and magnesium.
cauda equina: A bundles of nerve roots that look like a horse's tail, located at the end of the spinal cord.
causalgia: Intense, long-lasting burning pain usually caused by damage to a peripheral nerve.
cavity: A hole in the tooth caused by advanced decay.
CBC: Abbreviation for complete blood count—tests run on a blood sample to provide information on red cells, white cells, and platelets.
CCU: Abbreviation for coronary care unit, a ward in a hospital that provides specialized care and extensive monitoring for patients with heart problems.
celiac disease: A disease characterized by damage to the small intestine caused by an oversensitivity to gluten, a protein found in wheat, rye, and barley. Celiac disease can interfere with the proper absorption of nutrients from food.
celiac plexus: A network of nerves in the upper abdomen; medication is sometimes injected here as part of a therapy to ease pain called a nerve block.
cell: The basic building block of all living organisms.
cell senescence: The end stage in the life of a cell when the cell can no longer divide.
cell-mediated immunity: A type of immune response mounted against viruses, certain types of parasites, and perhaps cancer cells.
cementum: The layer of tooth material that covers the root.
central (brain) fatigue: A lack of concentration or alertness as well as a sense of lethargy and loss of motivation; involves the central nervous system.
central nervous system: The brain, brainstem, and spinal cord.
central sleep apnea: A disorder in which breathing repeatedly stops during sleep, because the brain doesn't properly signal the muscles that control breathing.
cerebellum: The part of the brain that controls coordinated movement.
cerebral aneurysm: A weakening and ballooning of the wall of an artery in the brain.
cerebral angiography: An invasive imaging procedure used to make detailed x-ray pictures of the blood vessels in the brain; dye is injected into the carotid arteries to highlight the blood vessels on x-rays.
cerebral cortex: The part of the brain involved in all forms of conscious experience, including thought, language, and memory.
cerebral hemorrhage: Bleeding in the brain caused by the rupture of a blood vessel; another term for hemorrhagic stroke.
cerebral infarction: A type of stroke caused when a blood vessel that supplies blood to the brain is blocked by a blood clot.
cerebrovascular: Pertaining to the blood vessels in the brain.
cerebrovascular accident: The medical term for a stroke.
cerumen: A substance that helps keep dirt out of the ear and lubricates the skin in the ear. More commonly known as earwax.
cervical radiculopathy: A pinched nerve, causing sharp pain, tingling, and numbness in the areas served by the nerve.
cervical spine: The part of the spine located in the neck and consisting of the top seven vertebrae.
cervical spondyloarthropathy: Inflammatory arthritis involving the neck portion of the spine.
cervicogenic headache: Headache related to neck problems. Also called cervical headache.
CFS: Abbreviation for chronic fatigue syndrome, a disorder of ongoing, severe tiredness that interferes with a person's ability to function well, isn't improved with rest, and isn't caused by another illness.
challenge testing: A way of testing for food allergy, usually in double-blind experiments in which neither patient nor doctor knows which food is taken in pill form.
chemical peel: A chemical solution applied to the skin to cause it to blister and peel, revealing a new layer of skin; treatment is used to improve the appearance of the skin, reducing lines, wrinkles, age spots, and other problems.
chemonucleolysis: A treatment for low back pain that involves injecting the enzyme chymopapain into a herniated disk.
chemoprevention: Using drugs or chemicals to prevent cancer.
chemotherapy: The use of chemicals to treat disease; often used to destroy cancer cells.
Cheyne-Stokes respiration: Abnormal breathing where cycles of deep, labored breathing where cycles of deep, labored breathing are followed by cycles of weak breathing that can result in a total, temporary lack of airflow.
chiropractor: Someone who treats disease by manipulation and adjustment of body structures, often the spine.
chlorophyllin: A chemical found in green, leafy vegetables thought to help prevent cancer.
chlorosis: Severe iron-deficiency characterized by a yellow-green tinge to the skin.
cholagogue: A substance that causes the gallbladder to squeeze, increasing the discharge of bile.
cholecystokinin: A hormone that signals the gallbladder to contract, releasing bile, and causes the pancreas to release enzymes used in digestion.
choleretic: An agent that promotes bile production.
cholesterol: A waxy, fat-like substance produced by the liver and found in all food from animal sources; an essential component of body cells and a precursor of bile acids and some hormones.
cholinergic neuron: A nerve cell that produces acetylcholine.
chondrocalcinosis: Arthritis caused by calcium crystals.
chondrocyte: A cartilage cell.
chondromalacia: A painful condition caused by irritation to or wearing away of the cartilage on the underside of the knee cap; known as runner's knee.
choroid: A thin layer of blood vessels and connective tissue between the white of the eye (sclera) and the retina.
chromosome: A threadlike structure, found in the nucleus of each cell, that carries almost all of a cell's genes.
chronic: Any condition that lasts a long time or recurs over time.
chronic fatigue syndrome: A disorder of ongoing, severe tiredness that interferes with a person's ability to function well, isn't improved with rest, and isn't caused by another illness.
chronic kidney disease: Any type of kidney disease that lasts longer than three months and impairs kidney function.
chronic pain: Pain that persists after an injury has healed or a disease is over.
chronic pain syndrome: Long-term, severe pain that doesn't spring from an injury or illness, that interferes with daily life, and is often accompanied by other problems, such as depression, irritability, and anxiety.
chronic paroxysmal hemicrania: Severe, frequent, short-lasting migraine-like headache attacks.
chylomicron: A fat globule that ferries triglyceride from the intestine to the liver and fat tissue.
chyme: A nearly liquid mass of partly digested food and digestive juices; found in the stomach and intestine.
cicatricial alopecia: A group of inflammatory hair disorders that can cause irreversible damage to the follicle that results in permanent hair loss and scarring. Also known as scarring alopecia.
cilia: Small, hairlike structures on the surface of some cells.
ciliary body: Part of the eye that produces the aqueous humor (fluid that nourishes the eye) and contains the ciliary muscle, which controls focusing of the lens.
circadian rhythm: The body's biological clock that regulates the sleep/wake cycle and other physiological processes.
Circle of Willis: A circle of arteries at the base of the brain, connecting major brain arteries and supplying blood to all parts of the brain.
cirrhosis: A chronic disease of the liver that progressively destroys the liver's ability to aid in digestion and detoxification.
CK: Abbreviation for creatine kinase, an enzyme found in the heart, brain, and skeletal muscle. Levels of creatine kinase are tested to diagnose certain illnesses.
classic migraine: A migraine headache preceded by visual disturbances; also known as a migraine with aura.
claudication: A muscle cramp, usually felt in the calf, caused by poor blood flow to the legs.
clinical trial: A study that tests a therapy in humans, rather than in laboratories or on animals.
clonal expansion: An explosive increase in the number of fighter cells released by the immune system to fight a threat in the body.
clot buster: Medications that dissolve blood clots and restore blood flow through a blocked artery.
cluster headache: A short-lived, extremely painful headache that occurs repeatedly over a period of a few weeks or months and then disappears for months or years.
coagulate: The process where a liquid, such as blood, comes together to form a soft, semi-solid mass, like a clot.
coarctation: A narrowed area in the aorta (the main artery that leaves the heart) present from birth.
cochlea: Part of the ear that converts sound into electrical signals that the brain interprets as a particular sound.
cochlear implant: A small electronic device that is implanted in the inner ear to restore some hearing to a deaf person.
coenzyme: A small organic molecule, often made from B vitamins, that helps enzymes function in the body.
cognitive behavioral therapy: A form of therapy that aimed at recognizing and changing negative thoughts and behaviors.
cognitive function: All of the brain mechanisms involved with thinking, reasoning, learning, and remembering.
cognitive impairment: Problems with memory, language, thinking, or other brain functions, varying from mild to serious difficulty.
cognitive reserve: The capacity of the brain to use alternative neural pathways or thinking strategies in response to neurological injury from conditions such as Alzheimer's disease.
colic: Severe abdominal pain caused by spasms in the intestines or in a portion of the kidneys.
collagen: A fibrous protein that is the main component of connective tissue in the body.
collagenase: An enzyme that breaks down collagen.
collateral circulation: A system of minor arteries, known as collaterals, that can serve as an alternate blood supply to the heart when a major coronary artery is blocked.
Colles fracture: A break at the end of the main bone of the forearm, the radius.
colon: The large intestine; a muscular tube that is 5 to 6 feet long. It compacts and moves solid waste.
colonoscopy: A procedure to see inside the colon, using a long, lighted flexible tube mounted with a tiny camera.
colorectal adenoma: A growth on the colon or rectal wall that may develop into cancer.
colostomy: Surgery that brings one end of the large intestine out through an opening in the abdomen for elimination of stool.
colostrum: An antibody-rich form of breast milk, produced at the end of pregnancy and for a short time after birth, which strengthens a newborn's immune system.
coma: Deep unconsciousness where the person is alive but unable to move or respond.
combined hormone therapy: Estrogen combined with progestogen, prescribed to augment a woman's depleted hormones during menopause.
combined hyperlipidemia: A condition, usually inherited, in which LDL cholesterol and triglyceride levels are very high.
common migraine: A migraine headache without any visual symptoms, such as not a blind spot, beforehand. Also called a migraine without aura.
communicable disease: Any disease caused by bacteria, viruses, or other pathogens that is spread from person to person.
compact bone: Hard, tightly-packed tissue that forms the outer shell of bones. Also called cortical bone or lamellar bone.
complement system: Proteins that kill viruses, bacteria, and other microbes directly or flag them for destruction by white blood cells.
complete blood count: Often referred to as CBC. A broad panel of screening tests that examine different parts of the blood and can be used to diagnose anemia, infection, and many other diseases.
complicated grief: A prolonged, intense reaction to bereavement that affects one in 10 people who lose a loved one. Key signs are inability to accept the death; frequent nightmares and intrusive, upsetting memories; detachment from others; constant yearning for the deceased; and excessive loneliness. Sometimes called traumatic or chronic grief.
complicated migraine: A migraine where one or more of the symptoms, such as visual problems, linger for at least a day after the headache is gone.
compounding pharmacy: A pharmacy that mixes custom medications for patients and doctors.
compression fracture: The collapse of a bone, most often a bone in the spine (vertebra).
computed tomography: An imaging technique that uses a computer and x-rays passed through the body at different angles to create a detailed, nearly three-dimensional picture of the body.
conception: The start of pregnancy, when an egg is fertilized by a sperm.
conductive hearing loss: Hearing loss caused by a blockage in the middle ear that prevents sound waves from reaching the inner ear.
condyle: A rounded knob at the end of a bone.
cones: Cells in the retina that are sensitive to color and light.
congestion: An accumulation of mucus or of blood in an organ.
congestive heart failure: An older term for heart failure, a disorder caused by a decrease in the heart's ability to pump blood. Congestive heart failure referred specifically to the type of heart failure associated with the accumulation of excess fluid in the lungs or extremities.
conjugate vaccine: A type of vaccine made by attaching an antigen (a substance that the body deems harmful) to a protein. It is often used to immunize babies and young children.
conjugated equine estrogens: Estrogen medications produced from the urine of pregnant horses.
conjunctiva: The clear, thin membrane that covers the inside of the eyelid and the white part of the eyeball.
conjunctivitis: Swelling or infection of the thin lining on the inside of the eyelid and the white part of the eyeball.
connective tissue: A group of tissues in the body that provide internal support and bind other tissues in the body, including bone, cartilage, tendons, and ligaments.
consolidation: The process by which the brain transforms newly acquired information into long-term memories.
contact dermatitis: A rash or skin irritation that results when skin contacts an allergen or irritating substance.
continuous combined hormone therapy: Estrogen and progestogen taken daily by women whose estrogen levels are low, usually due to menopause or a hysterectomy.
continuous positive airway pressure: A therapy for obstructive sleep apnea in which a machine delivers a continuous stream of air which prevents the collapse of the airway during sleep.
contractile proteins: Proteins that help shorten the length of muscle cells, enabling them to contract.
contracture: Shortening of a muscle, usually because of disease or lack of use, that limits joint movement.
contrast medium: A fluid injected into the bloodstream or swallowed so that organs will show up on x-rays.
control group: A group of people in a medical study who receive either no treatment or the standard treatment, which is compared against a group who receive the treatment being studied.
controllers: Asthma medications taken daily to prevent or control symptoms.
contusion: A bruise. An injury that causes swelling, pain, and discoloration but doesn't break the skin.
convulsion: Rapid uncontrollable shaking of the body caused by muscles contracting and relaxing repeatedly.
corn: An area of hardened, thickened skin usually caused by friction.
cornea: The clear dome that covers the front of the eye.
coronary: Pertaining to the arteries that supply blood to the heart.
coronary angiography: A test that shows how blood moves through the blood vessels supplying the heart to identify narrowed arteries. It uses x-rays and the injection of a fluid called a contrast agent that can be seen on the x-rays.
coronary artery: Blood vessel that carries oxygen-rich blood to the heart muscle.
coronary artery bypass surgery: Surgery to improve blood flow to the heart by diverting blood around a blocked coronary artery.
coronary artery disease: A condition in which one or more of the arteries feeding the heart become so narrow in spots that blood flow is impaired or stopped entirely, causing chest pain or a heart attack. Often called heart disease or coronary heart disease.
coronary endarterectomy: Surgery to remove fatty plaque that has built up on the walls of a coronary artery.
coronary heart disease: A commonly used term for coronary artery disease, a condition in which one or more of the arteries feeding the heart become so narrow in spots that blood flow is impaired or stopped entirely, causing chest pain or a heart attack.
coronary spasm: Temporary constriction of an artery that supplies blood to the heart, slowing or stopping blood flow.
coronary care unit: A ward in a hospital that provides specialized care and monitoring for patients with heart problems.
corpus callosum: The large bundle of nerve fibers linking the left and right sides of the brain.
corpus cavernosum: Sponge-like tissue in the penis that fills with blood during sexual arousal, causing an erection.
corpus luteum: The egg follicle remnant left behind after an egg has been released during ovulation. The corpus luteum secretes the hormone progesterone to stimulate the growth of the endometrium.
corpus spongiosum: A cylinder of soft tissue surrounding a man's urethra and running the length of the penis.
corrugator muscle: One of the muscles that forms frown lines on the forehead.
cortex: The middle layer and main structure of the hair shaft, consisting mainly of compact bundles of the protein keratin.
cortical bone: Hard, tightly-packed tissue that forms the outer shell of bones. Also called compact bone.
corticosteroids: Steroid medications made to mimic hormones produced naturally by the adrenal glands. They are used to treat a wide range of health problems.
corticotropin-releasing factor: A hormone made in the brain that triggers the body's fight-or-flight reaction to external threats.
cortisol: One of a class of stress hormones released during the fight-or-flight stress response.
COX-2 inhibitors: Abbreviation for cyclooxygenase-2 inhibitors, medications that reduce pain and swelling by targeting a particular enzyme known as cyclooxygenase-2 (COX-2).
CPAP: Abbreviation for continuous positive airway pressure, a therapy for obstructive sleep apnea in which a machine delivers a continuous stream of air which prevents the collapse of the airway during sleep.
CPR: Abbreviation for cardiopulmonary resuscitation, a combination of chest compressions and mouth-to-mouth breathing that keep oxygenated blood circulating to the brain and tissues.
cranial arteritis: Inflammation and damage to blood vessels supplying blood to the head and neck. Also called giant cell arteritis.
craving: Intense, often irrepressible urge for something; often a symptom of dependence on drugs, alcohol or addiction.
C-reactive protein: A protein made by the liver. High amounts of C-reactive protein may indicate that arteries are clogged (atherosclerosis).
creatine kinase: An enzyme that leaks into the bloodstream in high amounts if a muscle is damaged. Can be used to detect heart attack or muscle damage from other diseases.
creatinine: A waste product created by muscle metabolism. Doctors sometimes test creatinine levels to examine kidney function.
creatinine test: A blood or urine test that helps doctors determine if the kidneys are working properly.
crepitus: Grating, grinding, or popping sound or feeling made when a joint is moved.
Creutzfeldt-Jakob disease: A rare, untreatable, rapid form of dementia that is fatal.
Crohn's disease: A chronic disease that causes swelling of the digestive tract, pain, and diarrhea.
crown: The part of the tooth that is visible above the gum line. Also a restoration that covers the crown of the tooth.
cryotherapy: Use of extreme cold to freeze and destroy diseased tissue.
CRP: Abbreviation for C-reactive protein, a protein made by the liver. High amounts of C-reactive protein may indicate that arteries are clogged (atherosclerosis).
crystalline lens: Part of the eye that changes shape so that the eye can focus on objects at different distances.
CT: Computerized x-rays that provide detailed views of the body and brain. Also known as a computed tomography (CT) scan.
CT angiography: Use of a CT scan and an injectable dye to show arteries and blood vessels in detail.
cubital tunnel syndrome: The pinching of a nerve at the elbow, causing numbness in the pinkie and ring fingers and part of the hand.
cupping: An indentation in the optic disc that grows abnormally large with glaucoma.
curettage: Using a spoon-shaped instrument to remove diseased tissue or sample tissue.
Cushing's syndrome: A disorder caused by high levels of the stress-hormone cortisol resulting in damage to the body, including abdominal obesity, rounded red face, and other symptoms.
cuticle: The outermost, single-cell layer of the hair shaft.
cyanosis: A condition in which skin turns blue due to a lack of oxygen in the blood, often because of heart failure or lung disease.
cyclic guanosine monophosphate: A chemical in the body that widens blood vessels in the penis. This increases blood flow to the penis, causing an erection.
cyclic hormone therapy: Use of estrogen and progestogen for 10–14 days of the month to relieve symptoms of menopause.
cyclooxygenase: An enzyme that helps blood cells known as platelets stick to each other, a key step in the formation of a blood clot.
cyst: An abnormal growth in the body that is noncancerous.
cystoid macular edema: An eye condition in which the retina (the macula) becomes swollen with fluid.
cytokines: Proteins in the body that act as messengers between immune system cells.
cytotoxic alopecia: Drug-induced hair loss that occurs some weeks after the start of chemotherapy; hair grows back after cessation of treatment.
D2 receptor: A type of dopamine receptor (see neurotransmitter receptors) that seems to be particularly important in addiction.
daidzein: A substance found in soybeans.
daily value: A guide to the amount of nutrients in a given food; Daily values are given in percentages based on a 2,000-calorie-per-day diet.
dandruff: A mild and common condition that is characterized by an itchy, flaky scalp and that may extend to the ears, face, and chest. Also known as seborrheic dermatitis.
de Quervain's tendonitis: Painful swelling of the tendons at the wrist that move the thumb.
debility: Weakness or a loss of physical strength.
decibel: A unit of measurement for the loudness of a sound. The highest decibels indicate the loudest sounds.
declarative memory: Memory for facts or events (episodic memory); also called explicit memory.
decoction: An herbal product or tea made by boiling a plant in water.
decongestant: Type of medication used to relieve nasal congestion.
deep sleep: Stage of sleep where the brain is less responsive to outside stimuli.
deep venous thrombosis: A dangerous condition in which blood clots form in veins deep in the body, usually the legs. They may break off and block blood flow in the lungs, seriously damaging organs or causing death.
defenses: Coping strategies a person adopts to make it easier to operate in the world.
defibrillation: The delivery of an electric shock to the heart to stop an abnormal rhythm and restore a normal heartbeat.
defibrillator: A device that delivers an electric shock to the heart to restore normal rhythm. Used to treat cardiac arrest and other dangerous heart rhythm problems.
degenerative disease?: Any disease in which the organs or tissues in the body are damaged progressively over time.
degenerative disk disease: Normal, and sometimes painful, deteriorations in the disks of the spine that occur with age.
degenerative joint disease: Arthritis that occurs when the cartilage in joints breaks down over time; also called osteoarthritis.
degenerative spondylolisthesis: Arthritis of the spine that worsens over time; often caused by aging.
delayed sleep phase syndrome: A pattern of falling asleep and waking up later than wanted that tends to worsen progressively over time.
delirium: Sudden, severe confusion that occurs because of a mental or physical illness.
delta waves: Slow brain activity that occurs when a person is in deep sleep.
delusion: A false or irrational belief held by a person despite evidence to the contrary.
dementia: A loss of brain function that worsens over time and affects memory, thinking, behavior, and language.
dementia pugilistica: Loss of brain function, common among former boxers, caused by repeated blows to the head.
demineralization: The process by which bacteria destroy tooth enamel.
demulcent: A substance that soothes irritated tissues and mucous membranes.
dendrites: The parts of a nerve cell that receive signals from other nerve cells.
dendritic cells: Spidery-looking immune system cells that help protect the body from harmful substances.
denial: A defense mechanism characterized by the inability to recognize or admit that addiction is the cause of problems, rather than a solution or mere byproduct. Denial can also refer to the refusal to accept an upsetting reality, such as a serious illness or death or the feelings that follow either.
dental implant: A metal post inserted into the alveolar bone to support an artificial tooth or other prosthesis.
dentin: The layer of hardened tooth tissue under the enamel and around the pulp.
deoxyribonucleic acid: The substance found in the nucleus of cells that contains the genetic instructions for that living organism.
dermal papilla: A structure situated at the base of the hair follicle that contains nerves and blood vessels that fuel the cellular processes of the developing hair shaft.
dermatomyositis: A rare disease in which the muscles become weak and stiff and a skin rash appears.
dermis: The middle layer of skin that contains most of the skin's structures, like collagen, nerves, glands, and hair follicles.
desiccated thyroid: An extract made of dried animal thyroid glands.
detoxification: The process of removing harmful, or toxic, substances from a person's body.
detrusor instability: The sudden, strong need to urinate due to spasms in bladder muscles. Also called urge incontinence.
detrusor muscle: The layer of muscle in the bladder wall that squeezes urine out of the bladder.
detumescence: The softening of an erection.
diabetes: A disease in which the body does not properly produce or use insulin, resulting in abnormally high levels of sugar (glucose) in the blood.
diabetic ketoacidosis: A complication of diabetes in which substances called ketones build up in the blood to dangerously high levels.
diabetic retinopathy: A complication of diabetes that occurs when the small blood vessels in the retina are damaged. It can impair vision or even lead to blindness.
diaphragm: The dome-shaped sheet of muscle at the base of the lungs that helps move air in and out of the lungs.
diastole: The relaxation phase of the normal heart cycle.
diastolic blood pressure: The bottom number of a blood pressure reading, such as 134/78. It represents the pressure in the arteries when the heart relaxes between beats.
diastolic heart failure: The inability of the heart to relax properly between beats (diastole), making it difficult for the ventricles to fill completely with blood from the atria. This can occur when the heart muscle bulks up due to overwork or other causes or when the heart muscle stiffens and loses it flexibility.
diathermy: Use of high-frequency electric currents to heat deep muscle and joint tissue as a form of physical therapy.
dietary fiber: The part of plant foods the body can't digest or absorb. Also called roughage.
dietary reference intakes: The recommended amount of vitamins and minerals individuals should consume per day.
dietary supplements: Vitamins, minerals, herbs, and other substances taken in hopes of improving health.
digestive tract: The series of hollow organs, including the mouth, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus, which break down and digest food and expel waste.
digit: A finger or toe.
digital rectal examination: An exam in which a doctor inserts a lubricated, gloved finger into the rectum to check for abnormalities.
digitalis: A drug that increases the strength of heart muscle contractions.
dihydrotestosterone: A form of the hormone testosterone that spurs the prostate gland to enlarge (benign prostatic hyperplasia).
dilate: To widen or enlarge.
direct transmission: The immediate transfer of an infectious agent from a reservoir to a susceptible host by direct contact or droplet spread.
discoid lupus erythematosus: A rare form of lupus that causes a rash or scarring of skin.
disk: One of the small, shock-absorbing cushions found between the bones that make up the spinal column (vertebrae).
diskectomy: The surgical removal of part of a disk (a small, shock absorbing cushion located between the bones of the spinal column).
diskitis: Swelling of one or more of the pillow-like disks located between the bones of the spinal column.
dislocation: The movement of a bone from its normal position.
dithiolethione: A substance found in cruciferous vegetables, like cabbage, Brussels sprouts, and broccoli, which may play a role in cancer prevention.
diuretic: A drug that eases the heart's workload and decreases the buildup of fluid in the lungs and other parts of the body by promoting the excretion of water and salts. Diuretics (also called water pills) are used to treat high blood pressure, heart failure, and some congenital heart defects.
diverticulitis: The bulging out of small pouches or sacs of tissue from the colon wall.
diverticulum: A small pouch or sac of tissue that bulges out of the colon wall. The plural form is diverticula.
d-limonene: A substance found in citrus fruits.
DNA: An abbreviation for deoxyribonucleic acid, the substance in cells that contains the genetic instructions that direct their function.
DNR: Commonly used abbreviation for do-not-resuscitate order, a legal document that tells health professionals not to revive a person if his or her heart or breathing stops.
dominant: When the genetic trait carried by one allele of a gene pair eclipses the trait carried by another; for example, when a gene carries alleles for two different eye colors, the dominant eye color gene determines the person's eye color.do-not-resuscitate order: A legal document that tells health professionals not to revive a person if his or her heart or breathing stops. Commonly referred to as a DNR.
dopamine: A chemical messenger (neurotransmitter) that affects movement and thought processes.
Doppler ultrasound: A test that uses sound waves to measure how fast blood is flowing through blood vessels.
dorsal: Near the back of the body or an organ.
dorsal kyphosis: A rounded or curved back caused by spinal fractures from osteoporosis. Commonly called dowager's hump.
double blind: A medical study in which the researchers and participants don't know which group is receiving the medication or treatment being studied and which is getting a placebo (fake, inactive version of the medication).
double-contrast barium enema: An x-ray test done to check for colon cancer or other bowel diseases.
dowager's hump: A rounded or curved back (resembling a hump) caused by spinal fractures from osteoporosis.
doxazosin: Medication used to treat high blood pressure or an enlarged prostate gland.
Dressler's syndrome: Inflammation of the sac surrounding the heart (pericardium).
DRI: Abbreviation for dietary reference intake, the recommended amount of vitamins and minerals individuals should consume per day.
drusen: Tiny yellow deposits in the retina of the eye.
dry eye: Stinging, burning, or irritation that occurs when the eye doesn't produce enough moisture.
dry-powder inhaler: A small device that helps a person breathe in dry medication so it reaches the lungs.
dual energy x-ray absorptiometry: An x-ray test used to measure bone density and check for osteoporosis.
dual-photon absorptiometry: A test to measure bone density, usually in the spine or the hip.
duct: A tube or vessel in the body which carries the secretion of a gland; Secretion examples are tears, breast milk, etc.
duodenitis: Inflammation of the duodenum, which is the upper part of the small intestine.
duodenum: The upper part of the small intestine.
duplex Doppler ultrasound scanning: A tool that uses sound waves to reveal blood flow problems.
Dupuytren's disease: A condition that deforms the hand, causing fingers to curl toward the palm.
dura mater: A thin protective membrane covering the brain and spinal cord.
durable power of attorney: A legal document in which an individual appoints another person to make medical, financial, or other decisions when the individual becomes unable to make those decisions.
dysarthria: A speech disability caused by an injury to the brain centers controlling the face, mouth, neck, or throat. People with dysarthria may be able to understand speech and form the right words in their mind but cannot articulate them.
dyspareunia: Painful sexual intercourse.
dyspepsia: Pain or discomfort in the upper abdomen; upset stomach or indigestion.
dysphagia: Difficulty chewing and swallowing food. Dysphagia is extremely common after a stroke.
dysplasia: Abnormal changes in cells of a tissue. The cells aren't cancerous, but they can sometimes progress to cancer.
dyspnea: Difficulty breathing or shortness of breath.
dystonia: A disorder in which muscles twitch, causing uncontrollable twisting movements.
ear canal: A tube leading from the eardrum to the outer ear.
eardrum: A thin membrane separating the ear canal and middle ear.
earwax: A substance that lubricates the inner ear and helps protect it from dirt, damage, and infections.
EBCT: Abbreviation for electron-beam computed tomography, a high-speed imaging technology use to evaluate the heart and measure calcium deposits in arteries.
eccentric action: When muscles move joints by lengthening. Also known as cerumen.
ECG: An abbreviation for electrocardiogram, a test that measures the electrical activity of the heart and detects heart problems.
echocardiography: A diagnostic tool that uses high-frequency sound waves (ultrasound) to make images of the heart's size, structure and motion.
eclampsia: A serious condition related to high blood pressure that can threaten the life of a pregnant woman and her fetus.
ectopic pregnancy: Pregnancy in which a fertilized egg implants in an abnormal location outside the uterus, usually in the fallopian tubes. Ending the pregnancy is necessary.
ectropion: When an eyelid, usually the lower one, flips outward so that the inner surface is exposed.
eczema: A condition in which areas of the skin are dry, itchy, red, and cracked. Also known as atopic dermatitis.
ED: Commonly used abbreviation for erectile dysfunction, the inability to get or maintain an erection sufficient for intercourse.
edema: Swelling caused by abnormal accumulation of fluid in tissues.
EEG: Abbreviation for electroencephalogram, a test that measures the electrical activity of the brain and detects problems.
effusion: An abnormal buildup of fluid in a joint or tissue.
eighth cranial nerve: A nerve responsible transmitting sound and information about balance to the brain. Also called the auditory nerve.
ejaculation: A sudden discharge of a fluid from a duct; often used to describe the expulsion of seminal fluid from the urethra of the penis during orgasm.
ejection fraction: The percent of blood pumped out of the left ventricle with each heartbeat. A normal ejection fraction is in the range of 55% to 70%.
EKG: An abbreviation for electrocardiogram, a test that measures the electrical activity of the heart and detects heart problems.
elastin: A flexible, stretchy protein found in skin and connective tissue.
electrocardiogram: A test that measures the electrical activity of the heart and detects heart problems.
electroencephalogram: A test that measures the electrical activity of the brain and detects problems.
electrolysis: A permanent hair removal technique that destroys follicles one at a time with a hair-thin needle inserted into the base of the follicle.
electrolyte: Minerals in the body that are electrically charged and play an important role in body processes, such as regulating fluid levels in the body. Examples include calcium and sodium.
electromyography: A test that checks the health of muscles and the nerves that control them.
electron-beam computed tomography: A high-speed imaging technology use to evaluate the heart and measure calcium deposits in arteries. Sometimes referred to as EBCT.
electrophysiologic testing: A procedure used to provoke known or suspected arrhythmias.
elimination diets: A way of diagnosing food allergies in which suspected foods are removed from the diet one at a time until the food causing a problem is found.
ellagic acid: A chemical found in certain plants, such as raspberries and strawberries, that might help protect against cancer.
embolic stroke: A type of stroke that occurs when a blood clot that has formed elsewhere in the body breaks off and travels through the bloodstream until it blocks an artery that normally supplies blood to the brain.
embolism: Blockage of a blood vessel by a clot (an embolus) that has traveled from another part of the body.
embolus: A blood clot or particle that forms in one part of the body then moves through the bloodstream and lodges in a blood vessel elsewhere, blocking blood flow.
emetic: Any drug or other substance used to cause vomiting.
EMG: Abbreviation for electromyography—a test that checks the health of muscles and the nerves that control them.
emission: The discharge or release of a substance, usually a fluid.
emmenagogue: Herbs that stimulate menstrual blood flow.
enamel: The hard outside layer of tooth material.
encephalitis: A severe and sometimes deadly inflammation of the brain that can be caused by a number of different viruses.
encoding: A multistage process by which sensation, perception, or thought is transformed into neural representations that can be stored in memory.
endarterectomy: Surgical removal of plaque or blood clots in an artery.
endemic: Continually present among people in a geographic region.
endocarditis: An inflammation of the heart lining or valves, usually caused by bacterial infection.
endocardium: The inner layer of the wall of the heart.
endogenous opioids: Painkilling substances made by the body.
endometrium: The lining of the uterus.
endorphins: Substances in the body that reduce pain and create a feeling of well-being.
endoscope: A thin, flexible tube equipped with a light and camera that is used to see inside an organ or body cavity.
endoscopy: Inserting a flexible tube equipped with a light and camera into the body to see inside a body cavity or organ.
endothelins: Proteins that cause blood vessels to narrow and blood pressure to rise.
endothelium-derived relaxing factor: Chemicals in the body that cause blood vessels to expand or relax, lowering blood pressure. Often referred to as EDRF.
end-stage renal disease: Complete, or nearly complete, kidney failure. Dialysis or a transplant is needed for survival.
enkephalin: A chemical produced in the brain that reduces pain.
enteric nervous system: Part of the nervous system that controls the gastrointestinal system.
enteropathic: Disease affecting the intestinal tract.
enthesis: A place where a ligament, tendon, or muscle attaches to bone.
entropion: An eyelid, usually the lower lid, which folds inward so that the eyelashes rub against and irritate the surface of the eye.
enzyme: A substance that speeds up another chemical reaction. For example, digestive enzymes help speed up the digestion of food.
eosinophils: White blood cells that play an important role in allergic reactions.
epicardium: The outer layer of the wall of the heart.
epicondylitis: Pain and swelling in the tendons in the elbow, usually because of overuse.
epidemic: The occurrence of more cases of disease than expected within a population in a geographic area over a set period of time.
epidemiological study: An investigation of the links between certain behaviors or risk factors and the occurrence of disease or good health in a population.
epidermis: The outermost layer of skin.
epidural space: The space between the spinal cord and the bones of the spinal column where painkillers are injected.
epinephrine: A chemical that narrows blood vessels, increases heart rate, and helps trigger the fight-or-flight response to danger. Also called adrenaline.
EpiPen: A device used to inject a dose of medication (epinephrine) when a severe allergic reaction occurs.
epithelial cells: Cells which line organs and structures in the body, protecting or enclosing them.
epithelium: A layer of cells which lines organs and structures in the body, protecting or enclosing them.
erectile dysfunction: The inability to get or maintain an erection sufficient for intercourse. Sometimes referred to as ED.
erector spinae: A group of muscles and tendons in the back.
ergonomics: Designing and arranging work objects so that the user is comfortable, efficient, and less likely to be injured.
ergots: Substances derived from or made from a fungus; often used to treat headache.
eructation: The act of bringing up air from the stomach through the mouth with a characteristic sound. Commonly known as belching.
erythema: Redness of the skin because of widening of capillaries just below the surface of the skin.
erythema nodosum: Painful, red lumps beneath the skin; associated with Crohn's disease.
erythrocyte sedimentation rate: A test involving red blood cells; used to check for different infections, inflammations, and cancers.
erythropoietin: A hormone that controls red blood cell production.
esophageal manometry: A test to measure the pressure inside the lower part of the esophagus.
esophagitis: Irritation and swelling of the esophagus.
esophagus: The tube that carries food and liquids from the mouth to the stomach.
essential fats: Two fatty acids, omega-3 and omega-6, that the body needs for good health but can't make so they must come from foods and supplements.
essential hypertension: High blood pressure with no known cause; also called primary hypertension.
esterified estrogens: Artificially made hormones used to manage menopausal symptoms.
esthetician: A person who specializes in non-medical skin care and beauty treatments.
estradiol: The primary form of the sex hormone estrogen produced by women.
estrogen: The main sex hormone in women.
estrogen receptor: A site on the surface of some cells to which estrogen molecules attach.
estrogen-replacement therapy: Use of medications containing the sex hormone estrogen by women to replace naturally-occurring estrogen lost during menopause.
etidronate: A medication used to treat bone loss due to Paget's disease.
eustachian tube: A tube connecting the middle ear and the back of the nose that lets air into the middle ear.
euthyroid: Having a thyroid gland that works properly.
excitatory neurotransmitter: A chemical that forwards a message from one neuron to another.
excitotoxin: A brain chemical that damages neurons.
executive functions: The component of thinking that organizes, plans, decides, and inhibits inappropriate impulses.
exercise: A structured program of physical activity that helps an individual become physically fit.
exercise stress test: The use of a treadmill, stationary bicycle, or other exercise machine while hooked up to heart-monitoring equipment. The test is used to determine if the heart's blood supply is sufficient and if the rhythm remains normal when the heart is stressed.
exophthalmos: A protrusion or bulging of the eye that occurs with Graves' eye disease. Tissues behind the eye swell, forcing the eyeball forward. Also called proptosis.
exostosis: Abnormal bony growths in the ear caused by swimming regularly in cold water. Sometimes called surfer's ear.
experience sampling: A research technique for learning about people's activity patterns and psychological processes that involves paging them at random times to obtain brief reports.
expression hopping: A common phenomenon whereby people jump to a different expression of addiction. For example, people with heroin addiction might transition to alcohol addiction. Hopping is especially common during the recovery process.
expression of addiction: The specific way in which a person manifests addiction, for example, through the use of cocaine, or compulsive gambling.
extend: To straighten out a joint (for example, extending the arms overhead).
external otitis: An infection or irritation of the outer ear, ear canal, or both. Also called swimmer's ear.
extracapsular cataract surgery: A surgical technique to remove a cataract from the eye.
extract: A product made from substances that are drawn out of a plant or herb.
extraocular muscles: Six paired muscles that direct the eyes' circular, side-to-side, and up-and-down movements.
extrinsic factor: An outside factor that has an effect on a person's environment or well-being.
facet joints: Paired joints that link a vertebra to its neighboring vertebrae. They allow the spine to move as a unit.
facet rhizotomy: Surgical destruction of certain nerves and nerve roots to relieve pain.
false negative: Test results that show that a disease or substance isn't present, even though it is.
familial combined hyperlipidemia: An inherited disorder in which the liver overproduces very low-density lipoprotein, causing high levels of cholesterol or triglycerides, or both.
familial hypercholesterolemia: An inherited disorder in which the liver cannot properly remove low-density lipoprotein particles from the blood, causing a very high cholesterol level.
fasting lipid profile: A laboratory test to determine the relative levels of high-density lipoprotein, low-density lipoprotein, and total cholesterol in the blood. Also referred to as a lipoprotein analysis, full lipid profile, or cholesterol profile.
fasting plasma glucose test: A blood test that determines the amount of sugar (glucose) in the blood after an overnight fast of at least eight hours.
fast-twitch fiber: One of two main types of skeletal muscle fibers. Fast-twitch fibers are recruited most heavily when bursts of power are needed, as in sprinting. See also slow-twitch fiber.
fat: One of the three major nutrients, along with carbohydrates and proteins.
fatigue: A lack of energy. A decrease over time in the ability to perform a physical or mental task.
fatty acids: Components of fats that can be used for energy by cells.
fatty streak: The first stage of atherosclerosis, a build-up of fatty materials in the wall of a blood vessel.
febrile: Feverish; having a high body temperature.
fecal impaction: A mass of dry, hard stool that gets lodged in the rectum.
fecal occult blood test: A test that checks for colorectal cancer by detecting blood in the stool.
femur: Thigh bone.
ferritin: A protein that captures and stores iron.
fetal alcohol syndrome: A collection of birth defects resulting from exposure of the fetus to alcohol during pregnancy.
fiber: A substance found in plant foods that the body can't digest.
fibrillation: Rapid and uncoordinated contractions of heart muscle fibers. When this occurs, the heart can't properly contract or pump blood.
fibrin: A stringy protein that is the primary component of a blood clot.
fibrinogen: A protein that helps stop bleeding by aiding in forming blood clots.
fibroadenoma: A tumor that is not cancer; usually found in the breast.
fibroblast: A cell that helps form the collagen and elastic fibers of connective tissue.
fibroid: A tumor that is not cancer, which is found in the uterus.
fibromyalgia: A condition causing pain and tender spots throughout the body.
fibrous plaque: A buildup of fat on the inside of a blood vessel that interferes with blood flow.
fibula: The calf bone.
filtering procedure: A procedure to treat glaucoma in which a surgeon creates a drainage hole in the eye to relieve pressure.
finasteride: A medication for treating benign prostatic hyperplasia (enlargement of the prostate gland).
fixed joint: An area where two bones meet that is fixed, or doesn't move.
flaccid: Soft, not erect.
flare: Reappearance or worsening of symptoms.
flat feet: A condition in which the arch is flat all the time or flattens when bearing weight.
flatulence: Excess gas in the stomach or intestines that is expelled from the anus.
flatus: Gas expelled through the anus.
flavonoids: Chemicals found in fruits, vegetables, wine, and tea that may protect cells from damage and have health benefits.
flex: Bend a joint (for example, flexing the knees).
flexibility: A component of physical fitness that refers to the range of motion available at a joint.
flight-or-fight response: Changes that occur in the body, such as rapid breathing and heartbeat, when a person is confronted with a perceived physical or emotional threat. Also called the stress response.
floaters: Tiny spots or lines that appear in a person's field of vision when the jelly-like fluid of the eye breaks down with age. They are usually harmless, but can signal serious eye problems.
flow: A term coined by positive psychology pioneer Mihaly Csikszentmihalyi to describe an effortless, active state of being during which one loses awareness of time, self, and distractions. Flow hinges on balancing the size of a challenge and the level of skill a person brings to it.
fluorescein angiography: A test that uses special dye and a camera to examine blood flow in the retina.
fluoride: A mineral that protects teeth from decay and cavities.
fluoroscopy: A test that gives moving images of the inside of the body; could be likened to an x-ray movie.
foam cells: Lipid-laden cells, named for their foamy appearance under the microscope. As foam cells build up on the inside of blood vessel walls, they form a plaque that can block blood flow.
focal neuropathy: Damage to a specific nerve, causing pain or numbness.
focus words: Peaceful, relaxing words or phrases used during stress relief exercises.
follicle: A group of cells that form a small sac.
follicle-stimulating hormone: A hormone released by the pituitary gland that stimulates the production of eggs in women and sperm in men.
follicular unit: A small bundle that includes one to four follicles, oil glands, a tiny muscle, and other tissue.
follicular unit transplantation: Transplantation of follicular units, which mimic natural hair growth.
folliculitis: An inflammation of the hair follicle.
food allergies: Sensitivities to certain foods that can cause symptoms ranging from the mild (like hives) to the life threatening (such as anaphylaxis).
forehead lift: Cosmetic surgery to minimize creases on the forehead and between the eyebrows, and to lift sagging eyebrows.
fovea: A small dimple in the middle of the retina that provides sharp central vision.
fracture: A break in a bone.
FRAX tool: An algorithm for estimating the probability of breaking a bone because of low bone mass over a period of 10 years.
free fragment: Part of a disk in the back that has broken off from the main portion of the disk.
free radical: An unstable molecule in the body that plays a role in aging and can damage tissue; antioxidants help prevent free radical damage.
frequency: The pitch of a sound; measured by the speed at which sound waves vibrate.
frequency range: How much amplification a hearing aid produces in both high and low frequencies.
frequency response: The amplification that a hearing aid produces across different sound frequencies.
frontal lobe: Part of the brain that plays a role in determining consequences and choosing behaviors.
frontotemporal lobar degeneration: A brain disorder that can cause dementia, aphasia, neurotic behavior, and gradual changes in personality and emotional control.
frozen shoulder: Inflammation of various tissues of the shoulder, along with growth of abnormal bands of tissue that cause the shoulder to become so stiff that movement is severely limited.
fructose: A simple sugar found in corn syrup, honey, and many sweet fruits.
FSH: Abbreviation for follicle-stimulating hormone, a hormone released by the pituitary gland that stimulates the production of eggs in women and sperm in men.
functional gastrointestinal disorders: Gut problems that aren't caused by an infection or structural problem with the gastrointestinal system.
functional incontinence: Recognition of the need to urinate but being unable to get to the bathroom in time due to mental or physical problems, such as limited mobility.
fundoplication: Surgery that restructures the stomach to prevent acid reflux.
fundus photography: Imaging test that provides multi-dimensional pictures of the back of the eyeball.
fungus: Organisms and microorganisms, such as yeasts and molds, that can live as a parasite on plants and animals.
gain: A hearing aid's power, measured in the number of decibels that it can add to sound.
gait cycle: The cycle that the feet and legs make when walking, beginning when one heel hits the ground and ending when the same heel hits the ground again.
galactogogue: A substance that promotes breast milk production.
gamma-aminobutyric acid: A chemical messenger in the brain that may help decrease anxiety and promote slow-wave sleep. Often referred to as GABA.
ganglion: An abnormal but harmless mass of tissue, usually nerve cells.
ganglion cyst: A harmless sac of fluid on top of a joint or tendon, usually on the wrist or back of the hand.
gangrene: Death of tissue in part of the body because blood has stopped flowing there.
gastric: Relating to the stomach.
gastritis: Inflammation of the lining of the stomach.
gastroesophageal reflux disease: A condition in which food and acid flow back into the esophagus from the stomach, causing heartburn.
gastrointestinal: Relating to all or some of the organs of the digestive tract, from the mouth to the anus.
gastrointestinal tract: The digestive tract.
gene: Structures on chromosomes that are passed from parent to child. The basic unit of material that passes traits from parent to child.
gene therapy: Correction of a genetic defect by replacing an abnormal gene with a normal gene.
generic drug: A copy of a brand-name drug whose patent has expired. These drugs are less expensive than brand-name drugs.
genetic: Referring to inherited characteristics or genes.
genistein: An antioxidant chemical found in certain plants, like soybeans.
GERD: Abbreviation for gastroesophageal reflux disease, a condition in which food and acid flow back into the esophagus from the stomach, causing heartburn.
geriatric care manager: A trained medical professional who helps families who are caring for older adults.
geriatrician: A physician who specializes in the care of older patients.
gestational diabetes mellitus: A form of diabetes that appears during pregnancy.
GFR: Abbreviation for glomerular filtration rate, the rate at which the kidneys filter excess water and other wastes. A test by the same name is used to determine how well the kidneys are functioning.
giant cell arteritis: Inflammation and damage to blood vessels that supply the head and neck.
gingiva: Another term for gums: a form of oral tissue that covers the roots of teeth and surrounding bone.
gingivitis: Inflammation of the gums.
gland: Any organ or tissue that secretes fluids, such as hormones, for use elsewhere in the body or as waste.
glans penis: The head of the penis.
glaucoma: A condition in which the pressure inside the eye is too high, causing eye damage.
Gleason score: In men with prostate cancer, the Gleason score provides a rough estimate of how fast the cancer is growing.
glenohumeral joint: A shoulder joint that connects the ball of the humerus to the glenoid.
glenoid: The socket of the scapula that connects to the humerus at the shoulder.
glomerular filtration rate: The rate at which the kidneys filter excess water and other wastes. A test by the same name is used to determine how well the kidneys are functioning.
glomeruli: Tiny clusters of capillaries in the kidneys that filter waste products from the blood.
glucagon: A hormone produced in the pancreas that raises blood sugar levels.
glucocorticoids: Steroid hormones released by the adrenal gland when there seems to be a threat, and the stress response is triggered.
glucose: A simple sugar that is the body's main source of energy.
glucose intolerance: Blood sugar levels that are higher than normal, but not yet high enough for a diagnosis of diabetes.
glutamate: A chemical messenger in the brain that may play a role in mood disorders and schizophrenia.
glutamic acid decarboxylase: A protein found in beta cells, the cells that create insulin.
glycemic index: A ranking of foods according to how quickly and how much they raise blood sugar.
glycemic load: A ranking of how much a typical serving of a particular food will raise blood sugar.
glycogen: The body's fuel reserves. This substance, stored primarily in the liver and muscles, is later converted into glucose to provide cells with energy.
glycosylated hemoglobin: The product formed by the attachment of glucose (blood sugar) to hemoglobin (the oxygen-carrying protein in red blood cells). Usually referred to as hemoglobin A1c, or HbA1c.
GnRH: Abbreviation for gonadotropin-releasing hormone, a hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the pituitary gland.
GnRH antagonists: Drugs used to treat prostate cancer by blocking the release of luteinizing hormone that do not cause a temporary surge in testosterone.
goblet cells: Cells that produce mucus that line the gastrointestinal tract and lungs.
goiter: An enlarged thyroid gland that creates a lump in the neck.
gonadotropin-releasing hormone: A hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the pituitary gland.
gonioscopy: A test used to detect glaucoma that examines the area where fluid drains out of the eye.
gout: A form of arthritis that occurs when uric acid builds up in the joints; The big toe, knee, and ankle joints are most often affected.
graft: Transplanting tissue from one part of the body to another.
gram: A metric unit of weight equivalent to one-thousandth of a kilogram.
Graves' disease: An autoimmune disease that causes the thyroid gland to produce too much thyroid hormone. It is usually accompanied by an enlarged thyroid gland and swollen, bulging, red eyes that appear to stare, as well as occasional double vision and vision loss.
greenstick fracture: A fracture in a young, soft bone in which the bone bends and breaks only on the outer edge of the bend.
grief: A broad range of reactions to bereavement, including sadness, tears, shock, confusion, and anger, among others.
growth factor: A substance produced by the body to stimulate tissue growth.
G spot: The area of sexually sensitive tissue located on the roof of the vagina just inside the opening. Also known as the Grafenberg spot.
guardianship: A legal process of appointing a person to make decisions about important matters (such as health and finances) for someone who is unfit to make those decisions on his or her own.
gullet: The esophagus.
gum disease: Diseases including gingivitis and periodontitis that attack the gum tissue and the structures supporting the teeth. Also called periodontal disease.
gums: A form of oral tissue that covers the roots of teeth and surrounding bone. Also called the gingiva.
hair bulb: The root of the hair shaft.
hair cells: Cells in the ear that transmit sound messages to the brain and play a vital role in hearing.
hair shaft: The portion of hair that extends beyond the surface of the skin. It contains three layers: the cuticle, cortex, and medulla (not always present).
hallucination: A perception of something that is not really there.
hammertoe: A sometimes painful condition in which the toe curls up and under (resembling a hammer).
happiness: Feelings of contentment or joy; the overall experience of pleasure and meaning in life.
happiness set-point: An individual's baseline level of happiness, determined largely by genetics, around which moods fluctuate. After reacting to positive or negative life changes, people tend to return to their happiness set-points.
harm reduction therapy: A treatment strategy aimed at minimizing the harm associated with an object of addiction. This strategic approach helps people learn how to limit the degree to which they use their object of addiction, or limit the risks associated with their use, but they do not necessarily stop altogether.
Hashimoto's thyroiditis: A disease in which the body's immune system prevents the thyroid gland from producing enough thyroid hormone.
hay fever: A commonly used term for allergic rhinitis—seasonal or year-round allergic condition marked by sneezing, runny nose, and congestion. The most common type of allergy, it is caused by an IgE-mediated immune response to inhaled airborne allergens.
HbA1c: Abbreviation for hemoglobin A1c, the product formed by the attachment of glucose (blood sugar) to hemoglobin (a protein in red blood cells). A test for HbA1c is a useful measure of blood sugar control.
HDL: Abbreviation for high-density lipoprotein, the so-called good cholesterol. This lipoprotein (a substance made up of fats and protein) is believed to remove cholesterol from the arteries.
health care proxy: A legal form allowing a person to appoint someone else to make their medical decisions. Also known as a durable power of attorney for health care.
hearing aid: An electronic device worn in or behind the ear by people with hearing problems that makes sounds louder.
heart attack: The common term for a myocardial infarction. It refers to the damage that occurs when blood flow to part of the heart is blocked or drastically restricted. The blockage usually stems from the rupture of an atherosclerotic plaque.
heart block: The difficulty or inability of the electrical signal that triggers a heart contraction to pass through the atrioventricular node.
heart failure: The inability of the heart to pump enough blood to meet the needs of the body's organs.
heart murmur: An extra or unusual sound heard during the heartbeat. A murmur may or may not be a sign of a problem in the heart.
heart rate: The number of times the heart contracts in a minute, normally 60–100 times.
heartburn: A burning pain in the chest or throat, caused when stomach acid backs up into the esophagus.
Heberden's nodes: Bony bumps found on the finger joints in some people with osteoarthritis.
hedonic: Devoted to pleasure.
hedonic treadmill: The human tendency to adapt to new circumstances and eventually consider them to be normal, so the emotional effects (negative or positive) generated by a change fade over time.
heel spur: An abnormal growth of bone or calcium on the heel bone.
Helicobacter pylori: Bacteria that damages the lining the stomach. It is to blame for most ulcers and stomach inflammation. Often called H. pylori.
helper T cells: Cells that help fight disease by activating and directing other immune system cells.
hematemesis: The vomiting of bright red blood, indicating bleeding in the upper digestive tract.
hematoma: Blood that leaks out of blood vessels and collects in the body.
hematuria: Blood in the urine.
hemianopia: Poor vision or blindness in half of the visual field, affecting one or both eyes.
hemiparesis: Muscle weakness on one side of the body.
hemiplegia: Paralysis on one side of the body.
hemochromatosis: A genetic condition in which the body absorbs and stores too much iron.
hemodialysis: The use of a machine to remove wastes and impurities from the blood when the kidneys are not working properly.
hemoglobin: The oxygen-carrying substance that gives red blood cells their color.
hemoptysis: Coughing up or spitting up blood from the lungs.
hemorrhage: Bleeding from a damaged blood vessel.
hemorrhagic stroke: A type of stroke that occurs when a blood vessel leaks or bursts inside the brain, cutting off the supply of oxygen and nutrition to that part of the brain.
HEPA filter: Abbreviation for high-efficiency particulate air, a type of highly efficient air filter.
heparin: A drug that prevents blood from clotting.
herd immunity: Protection occurring when so many people in a region are immune to an infectious disease that it can't spread to others.
herniated disk: When part of a spinal disk bulges out of a tear or weak spot in the disk's tough outer shell. Also known as prolapsed disk.
herpes zoster: A painful blistering skin rash caused by the chicken pox virus; also known as shingles.
hertz: The measurement of a sound's frequency.
hiatal hernia: When part of the stomach pushes upward into the chest through an abnormal opening in the diaphragm.
high blood pressure: When blood flowing through arteries pushes on artery walls with abnormally high force over a sustained period of time. Also called hypertension.
high-density lipoprotein: So-called good cholesterol. This lipoprotein (a substance made of fat and protein) removes cholesterol from arteries.
high-intensity focused ultrasound: A treatment that destroys tumors with heat generated by ultrasound energy.
hippocampus: Part of the brain that plays an important role in processing long-term memories.
hirsutism: Excessive facial or body hair in women.
histamine: A substance released by the immune system when it is exposed to an allergen. Histamines cause many allergy symptoms.
HIV: Abbreviation for human immunodeficiency virus, the virus that leads to acquired immunodeficiency syndrome (AIDS). HIV damages immune cells so that they are no longer able to fight off other infections.
hives: An itchy rash of usually short duration. Also known as urticaria.
HLA: Abbreviation for human leukocyte antigen, a protein found on the surface of white blood cells that helps the body recognize and fight foreign substances.
Holter monitor: A small machine worn for a day or more to continuously record the heart's electrical activity. Holter monitors are used to help diagnose heart rhythm problems.
homeostasis: The body's ability to keep blood pressure, temperature, water levels, oxygen levels, and more set at the right levels for cells to survive.
homocysteine: An amino acid formed as part of the normal breakdown of protein.
homocystinuria: A rare genetic disease that causes blood levels of homocysteine to rise too high.
hormone therapy: Use of medications to boost levels of hormones that decrease with age.
hormones: Powerful chemicals that affect many processes in the body, including sexual function, mood, and growth.
host: A person or other living organism that can be infected by a virus or other pathogen under natural conditions.
hot flash: A sudden, intense, hot feeling in the face or upper part of the body, along with rapid heartbeat, sweating, and flushing. A symptom of menopause.
HPA: Abbreviation for hypothalamic-pituitary-adrenal axis, a system that controls many hormonal activities in the body, including the stress response.
human immunodeficiency virus: Usually abbreviated as HIV, the virus that leads to acquired immunodeficiency syndrome (AIDS). HIV damages immune cells so that they are no longer able to fight off other infections.
human leukocyte antigen: A protein found on the surface of white blood cells that helps the body recognize and fight foreign substances.
humectant: An agent used in moisturizers; binds water to the skin to promote hydration.
humoral immunity: Immunity from infection and disease that comes from the release of antibodies in the blood.
Huntington's disease: An inherited disorder characterized by involuntary jerky movements and dementia.
hyaluronic acid: A hydrating sugar secreted by cells.
hydrogen breath test: A test used to diagnose gastrointestinal problems; it measures the amount of hydrogen in the breath, which rise when food isn't being absorbed properly.
hydrogenation: The addition of hydrogen to a compound. Hydrogenation is used to solidify liquid vegetable oils. The process creates trans fats, which are harmful to the heart and blood vessels.
hydroxyapatite: A hard substance that is a major component of bones and teeth.
hygiene hypothesis: The theory that modern cleanliness means children are not exposed to as many germs at an early age, which results in a more allergies.
hyperaldosteronism: Overproduction of the hormone aldosterone, which causes the kidneys to retain sodium and water, often leading to high blood pressure.
hyperalgesia: An increased sensitivity to pain.
hypercholesterolemia: High levels of cholesterol in the blood.
hyperglycemia: An abnormally high amount of sugar in the blood.
hyperinsulinemia: High levels of insulin in the bloodstream.
hyperlipidemia: High levels of blood lipids (fats and waxes such as cholesterol).
hyperopia: Difficulty seeing objects that are nearby; farsightedness.
hyperparathyroidism: Overproduction by the thyroid glands of parathyroid hormone.
hyperplasia: Increased production of cells in a normal tissue or organ; may be harmless or a sign of precancerous changes.
hyperplastic polyp: Noncancerous growths commonly found in the colon and rectum.
hypertension: The medical term for high blood pressure. Hypertension is a major risk factor for stroke, especially hemorrhagic and lacunar strokes, because it puts excess stress on the walls of blood vessels and damages their delicate inner lining.
hypertensive cerebellar hemorrhage: A stroke in which there is bleeding in the cerebellum because high blood pressure has weakened arteries in the brain.
hypertensive intracerebral hemorrhage: A stroke in which high blood pressure causes a blood vessel deep in the brain to rupture.
hyperthyroidism: A condition in which the thyroid gland makes too much thyroid hormone.
hypertriglyceridemia: High levels of triglycerides in the blood. A normal triglyceride level is less than 150 mg/dL.
hyperuricemia: Abnormally high levels of uric acid in the blood.
hypnagogic hallucinations: Vivid dream-like sounds or images that occur while on the verge of falling asleep.
hypnogram: A diagram that summarizes the stages of sleep recorded in a sleep laboratory.
hypnotic: An agent that promotes and aids sleep.
hypoglycemia: A condition in which blood sugar drops to an abnormally low level.
hypogonadism: Extremely low levels of testosterone in circulation.
hypomania: A mild form of mania, in which a person has lots of energy, talks faster than normal, has racing thoughts, and elevated mood.
hypopnea: Breathing that is more shallow and slow than normal.
hypotension: The medical term for low blood pressure.
hypothalamic-pituitary-adrenal axis: A system that controls many hormonal activities in the body, including the stress response. Often called the HPA axis.
hypothalamus: A small area in the brain that produces hormones that control body temperature, hunger, moods, the stress response, and other key functions.
hypothyroidism: A disease in which the thyroid gland does not make enough thyroid hormone.
hypoxia: When all or part of the body doesn't get enough oxygen.
hysterectomy: An operation to remove a woman's uterus.
iatrogenic: Complications or poor effects caused by medical treatment.
IBD: Abbreviation for inflammatory bowel disease, a general term for two disorders—ulcerative colitis and Crohn's disease—that cause the intestines to become swollen and inflamed.
ICD: Abbreviation for implantable cardioverter defibrillator, a device implanted in the chest and connected to the heart that delivers a shock to stop a potentially deadly rhythm and restore a normal (sinus) rhythm.
ice pick headache: Stabbing, very intense headaches that come on suddenly and are very brief.
idiopathic: A condition or disease of unknown origin.
IgE: Abbreviation for immunoglobulin E, the substance responsible for most allergic reactions.
ileum: The final section of the small intestine.
iliopsoas muscles: Two muscles, running from the end of the spine to the thighbone, that are responsible for lifting the knee.
immediate hypersensitivity: A category of allergic reaction, triggered by specific allergens and involving IgE. The majority of allergic reactions to pollens, pets, dust, mold, food, and insect venom are of this type.
immobilize: To restrict the movement of a limb or other part of the body to help in healing.
immunity: The body's ability to resist infection and disease.
immunization: Injection of harmless bacteria or viruses to spur the body to produce antibodies so it can resist a particular disease.
immunoglobulin: Substances made by the immune system that attack foreign substances. Also known as antibodies.
immunoglobulin E: The substance responsible for most allergic reactions.
immunologically privileged site: A part of the body—such as the eye or ovaries—where the immune system isn't able to function because it may damage the tissue there.
immunosuppressant drug: Medication that stifles the body's immune response; often given after an organ transplant to prevent rejection of the new organ.
immunotherapy: Treating disease by enhancing or suppressing the body's immune system.
impacted: Something firmly fixed into place, such as a wisdom tooth.
impaction: A mass of hardened feces blocking the rectum or colon.
impaired fasting glucose: Blood sugar levels that are higher than normal but not yet diabetic. This term is used when the high blood sugar levels are found with a fasting plasma glucose test.
impaired glucose tolerance: Blood sugar levels that are higher than normal but not yet diabetic. This term is used when the high blood sugar levels are found with an oral glucose tolerance test.
impedance hearing testing: A test that sends sound waves to the eardrum to determine if a problem in the middle ear is causing hearing loss.
implantable cardioverter defibrillator: A device implanted in the chest and connected to the heart that delivers a shock to stop a potentially deadly rhythm and restore a normal (sinus) rhythm.
impotence: The inability of the penis to become firm or to stay firm enough to have sexual intercourse.
in situ: Latin for in place.
inactivated vaccines: Vaccines containing microbes that have been killed, and, therefore, are unable to cause disease.
incision: A cut made into the skin or an organ during surgery.
incontinence: Involuntary passing of urine or feces.
incubation period: The time between when a person is exposed to an infection and when symptoms appear.
infarct: An area of dead tissue caused by insufficient blood supply.
infarction: The death of tissue due to a lack of blood.
infection: The growth of harmful organisms that can cause disease, such as bacteria, in the body.
infectious arthritis: Arthritis caused by harmful organisms such as bacteria.
inferior myocardial infarction: Heart attack involving the back part of the heart-muscle wall.
inferior vena cava: The large vein that carries blood from the lower half of the body to the heart.
infiltrating cancer: A cancer that has spread from where it first developed into surrounding tissue.
inflammation: The body's reaction to injury or infection. It is characterized by swelling, heat, redness, and pain.
inflammatory bowel disease: A general term for two disorders, ulcerative colitis and Crohn's disease, that cause the intestines to become swollen and inflamed. Often referred to as IBD.
infusion: The slow injection of a fluid into a vein or tissues.
ingrown toenail: A condition in which the side of a toenail pierces the skin, causing pain, swelling, and sometimes infection.
inhibitory neurochemical: A chemical that stops the transmission of a message from one nerve cell to another.
injectable fillers: Substances injected into the skin to fill in wrinkles or add plumpness to the lips.
injection: Inserting fluids, such as medications, into the body by means of a hollow needle and syringe.
innate immunity: The body's basic defenses against disease or infection that are present from birth.
inner ear: The deepest part of the ear, consisting of the cochlea and the labyrinth.
inoperable: A condition that cannot be treated by surgery.
insomnia: The inability to fall asleep or remain asleep long enough to feel rested.
insulin: A hormone made by the pancreas that controls the amount of glucose (sugar) in the blood.
insulin resistance: A condition in which the body produces insulin but can't use it properly. This leads to diabetes.
insulin-dependent diabetes: Now called type 1 diabetes. It occurs when the body doesn't produce enough insulin to control blood sugar levels properly.
intense pulsed light: A device that emits broadband light to improve the look of the skin or remove unwanted hair.
intensity: In exercise, a measure of how hard the body is working. Cues like breathing, talking, and sweating help measure intensity through perceived exertion.
interferons: Proteins made by the body to protect against viruses, bacteria, and other harmful agents.
interleukins: A group of substances that act as messengers in the immune system.
intermediate-density lipoprotein: A type of lipoprotein. It consists of remnants of very-low-density lipoprotein (VLDL) that eventually turn into low-density lipoprotein (LDL).
intermittent claudication: Pain and cramping in the legs during exercise that is caused by narrowed or blocked arteries. Also known as peripheral artery disease of the legs.
international unit: An internationally accepted amount of a substance based on its biological activity or effect; used as a measurement for fat-soluble vitamins.
interpersonal therapy: Short-term talk therapy focused on identifying and addressing problems in current relationships and building social skills.
intervention: A planned, often group, meeting with a person with addiction, with the aim of overcoming denial and inducing the individual to seek treatment.
intervention study: A study that compares one group that receives a medication or other therapy (an intervention) and another group does not (controls).
intervertebral disk: One of the small, shock-absorbing cushions located between the vertebrae of the spine.
intervertebral foramen: The opening between vertebrae through which a spinal nerve exits the spinal column (plural: foramina).
intolerance: An adverse reaction that may have similar symptoms to an allergic reaction but does not engage the immune system, and thus is not an allergy.
intracerebral hemorrhage: A hemorrhagic stroke caused by the rupture of a blood vessel and subsequent bleeding into the brain tissue.
intraocular lens: A small artificial lens permanently fixed inside the eye to replace the natural lens during cataract surgery.
intrinsic sphincter deficiency: Inability of the urinary sphincter to close completely.
iodides: Salt compounds containing iodine that are used to control severe hyperthyroidism in special circumstances. They work by decreasing the thyroid gland's production and secretion of thyroid hormone.
iris: The colored ring in front of the lens that controls the size of the pupil and how much light enters the eye.
irritants: Substances such as tobacco, wood smoke, perfumes, and others that cause allergy-like symptoms, although the response is not an allergic reaction.
ischemia: Inadequate blood supply to an organ or part of the body.
ischemic heart disease: The most common form of heart disease, in which narrowed or blocked coronary arteries have difficulty supplying sections of the heart muscle with the blood they need (ischemia).
ischemic stroke: A stroke caused by an interruption in the flow of blood to the brain; almost always caused by a blood clot blocking a blood vessel.
islets of Langerhans: Clusters of hormone-producing cells, including alpha and beta cells, that appear throughout the pancreas.
isolated systolic hypertension: A form of high blood pressure (hypertension) characterized by elevated systolic blood pressure and normal diastolic pressure.
isometric: An action in which a muscle generates force but does not contract or extend enough to move a joint, such as when pushing against an immovable object.
isotonic: An actions in which a muscle generates force by contracting or lengthening to move an attached joint through its range of motion, such as lifting a dumbbell from knee-height to shoulder-height.
IU: Commonly used abbreviation for international unit, an internationally accepted amount of a substance based on its biological activity or effect; used as a measurement for fat-soluble vitamins.
jejunum: The section of the small intestine between the duodenum and the ileum.
jet lag: A feeling of fatigue that occurs as the biological clock resets itself after traveling across time zones, usually by airplane.
joint: A junction in the body where bones are linked together.
julienne: To cut food into thin, matchstick strips.
Kegel: An exercise that helps prevent and treat incontinence by strengthening pelvic floor muscles.
keloid: An unusually hard or thick scar that forms after surgery or an injury.
keratectomy: A procedure in which a laser is used to correct vision problems by reshaping the cornea.
keratin: A protein and the major component of the cuticle and cortex layers of hair; the same protein is found in nails, feathers, claws, and hooves.
keratinocytes: Cells of the epidermis that produce a tough protein called keratin and form a soft, protective sheet for the body.
keratoconjunctivitis sicca: Persistent dryness of the eye.
keratoderma blennorrhagica: A skin rash that sometimes occurs along with an autoimmune condition called Reiter's syndrome.
Keshan disease: Heart disease caused by a lack of selenium, an element that the body needs to function properly.
ketones: Substances produced when the body burns fat for energy or when the body doesn't have enough insulin.
kidney failure: The final stage of chronic kidney disease. At this point, the kidneys can no longer eliminate waste products from the body.
kyphoplasty: A surgical procedure that eases or eliminates the pain of spinal fractures. It also restores vertebrae that have collapsed due to fractures to their normal size.
labile hypertension: Blood pressure that frequently fluctuates between normal and abnormal during the course of a day, often within only a few minutes.
labyrinth: The inner ear. It contains the cochlea, which is responsible for hearing, as well as structures that are needed for balance.
laceration: A tear in the skin.
lacrimal gland: The gland that produces tears.
lactase: An enzyme that breaks down milk sugar (lactose) in the body.
lactic acidosis: A rare but potentially lethal condition in which blood lactic acid levels increase.
lactose: A sugar found in milk and dairy products.
lactose intolerance: The inability of the body to easily digest lactose, a sugar found in milk and dairy products.
lacunar stroke: A small ischemic stroke caused by the blockage of one of the smaller blood vessels in the brain; the most common effect is weakness or disability on one side of the body.
lamellar bone: Hard, dense tissue that forms the outer shell of bones. Also called compact bone.
lamina: One of the two thin, plate-like parts of each vertebra.
laminectomy: An operation in which all or part of one or both laminae is removed.
Langerhans cells: Cells of the immune system that work in the skin to fight infection.
lanugo: Fine, soft hair that grows all over the body of a fetus and is typically shed before birth.
laparoscopy: A surgical procedure carried out with tiny instruments inserted through small openings in the skin.
laser: A concentrated beam of light; lasers are used in certain surgeries and other medical procedures.
laser assisted uvula palatoplasty: A surgical procedure to ease snoring by removing or reshaping some of the tissues in the mouth (usually the uvula and soft palate) that vibrate and cause the noise of snoring.
laser hair removal: Permanent hair removal technique that uses a laser to target and heat melanin in the hair shaft, which damages the hair follicle.
laser photocoagulation: Surgery that uses a laser to seal off blood vessels in the eye; used to treat a number of eye diseases.
laser prostatectomy: A surgical technique for treating an enlarged prostate (benign prostatic hyperplasia). It uses a high-energy laser to remove large amounts of prostate tissue with little bleeding.
latex allergy: An allergic reaction to the proteins found in natural rubber.
laxative: A drug or substance that induces bowel movements or makes the stool softer and looser.
LDL: Abbreviation for low-density lipoprotein. This so-called bad cholesterol can build up on artery walls, narrowing the artery and making a heart attack or stroke more likely.
learned insomnia: When fear of not sleeping develops after a short period of not sleeping well, and this anxiety causes ongoing trouble falling or staying asleep.
LED photomodulation: Use of a panel of light-emitting diodes (LEDs) to stimulate skin cells and improve the look of the skin.
left anterior descending coronary artery: One of the main arteries that supplies blood to the heart; it runs down the front surface of the heart.
left atrium: The left upper chamber of the heart.
left circumflex coronary artery: One of the main arteries that supplies blood to the heart; it curves around the back of the heart.
left ventricle: The left lower chamber of the heart. It pumps blood out of the heart to other organs in the body.
left ventricular hypertrophy: A thickening of the wall of the lower left chamber of the heart, which is responsible for pumping blood to organs throughout the body.
left-ventricular assist device: A surgically implanted pump that augments the pumping action of the left ventricle.
lensometer: A device used to check the prescription of eyeglasses.
leptin: A hormone produced by fat cells that acts on the brain to suppress appetite and burn stored fat.
lesion: An infected, diseased, or wounded area of tissue.
leukotriene blockers: Asthma medications that work by blocking leukotrienes, chemicals made in the body as part of an allergic reaction.
leukotriene modifiers: Asthma medications that work by blocking the production or action of leukotrienes, chemicals made in the body as part of an allergic reaction.
leukotrienes: Chemicals that cause airways to swell when an allergic reaction occurs or in diseases like asthma.
levothyroxine sodium: A man-made version of the thyroid hormone thyroxine.
LH: Abbreviation for luteinizing hormone, a hormone that controls ovulation in women. In men, luteinizing hormone triggers production of testosterone.
libido: Sexual desire.
lice: A blood-sucking parasite known as Pediculus humanus capitis that can cause an itchy scalp; infestations are highly contagious and especially common in school-age children.
ligament: A band of tissue that connects bones.
ligature: Any material that is tied around a blood vessel to stop it from bleeding.
lignans: Antioxidant chemicals found in seeds like flax and sesame, as well as some fruits, vegetables, and grains.
limbic system: A group of structures in the brain that help control memory, emotions, sexual arousal, and motivation.
limbus: The border between the cornea and the white of the eye.
liothyronine sodium: A man-made version of the thyroid hormone triiodothyronine.
lipase: An enzyme secreted by the pancreas that helps the body break down fats.
lipids: Fats, oils, and waxes that serve as building blocks for cells or as energy sources. Lipids are also capable of accumulating in the artery walls to form plaque.
lipoatrophy: Dents or depressions in the skin that are caused by a loss of fatty tissue.
lipohypertrophy: A buildup of fatty tissue.
lipoma: A noncancerous tumor or growth composed of fat cells.
lipoprotein: A combination of fat (lipid) and protein molecules bound together as packages. The combination allows fats and cholesterol to move easily through the blood.
lipoprotein analysis: A test that measures the amount of triglycerides, total cholesterol, HDL (good cholesterol), and LDL (bad cholesterol) in a person's blood.
lipoprotein(a): A molecule made up of fat and protein that is very similar to harmful LDL.
liposuction: A cosmetic procedure that removes fat from an area of the body.
live attenuated vaccines: Vaccines made from a weakened virus or microbe. These weakened viruses and microbes don't cause disease; instead they teach the body to recognize the substance as harmful and destroy it if there is contact with it in the future.
liver: A vital organ that removes waste products from the body and helps with digestion.
living will: A legal document that states what a person would and wouldn't want if he or she is no longer able to make health care decisions.
lobar hemorrhage: Bleeding that occurs in the white matter of the brain beneath the cerebral cortex.
lobotomy: A surgical procedure to severe one or more branches of nerves into the frontal lobe of the brain.
lobules: Milk-producing glands of the breast.
localized: In reference to cancer, generally means cancer that is limited to a specific gland or other tissue, without any distant spread; an organ-confined cancer.
locus ceruleus: An area of the brain stem that helps control the brain's alertness, responses to certain stimuli, and stress and anxiety levels.
long-term memory: A memory that lasts from a few minutes to decades.
low-calorie diet: A weight-loss plan that limits calories to 800–1,500 a day.
low-density lipoprotein: So-called bad cholesterol. If there is too much LDL in the blood, it can collect on artery walls, narrowing them and making heart attacks and strokes more likely.
lower esophageal sphincter: A ring of muscle where the esophagus and stomach meet. It relaxes to let food into the stomach and closes to prevent stomach acids from backing up and irritating the esophagus.
lumbar puncture: A procedure in which a hollow needle is inserted into the lower part of the spinal canal to withdraw fluid for testing. Also called a spinal tap.
lumbar spine: The lower portion of the spine. It includes the five lowermost bones (vertebrae) of the spine and is the start of the lower back.
lumbar stenosis: Narrowing of the spinal canal in the lower portion of the spine (known as the lumbar spine).
lumen: The hollow part of a tube, like a blood vessel, or the cavity in a hollow organ.
lutein: A natural substance found in green leafy vegetables.
luteinizing hormone: A hormone that controls ovulation in women. In men, luteinizing hormone triggers production of testosterone.
luteinizing hormone-releasing hormone agonist: A drug that slows the production of hormones by the testicles in men or the ovaries in women.
LVAD: Abbreviation for left-ventricular assist device, a surgically implanted pump that augments the pumping action of the left ventricle.
Lyme disease: An infectious disease transmitted by a tick bite.
lymph nodes: Small, bean-shaped organs that filter germs and foreign matter out of the body. Also called lymph glands.
lymphatic system: A system of channels that drains excess clear fluid, called lymph, from tissues and returns it into the bloodstream.
lymphedema: Blockage in or damage to the lymphatic systems, causing lymphatic fluid to build up in tissues, making them swell.
lymphocyte: A type of white blood cell that can recognize foreign substances in the body.
lymphoma: A type of cancer that affects cells in the lymphatic system.
macrocytic anemia: The presence of larger-than-normal red blood cells in circulation—even though there are too few of them—caused by lack of folate and vitamin B12.
macronutrients: Substances that provide energy and that the body needs for growth. The main categories are: fat, carbohydrate, and protein.
macrophage: A type of white blood cell that destroys cell debris, bacteria, and foreign agents.
macula: The area in the center of the retina that produces sharp, clear central vision and allows one to see fine detail.
macular degeneration: An eye disease that slowly destroys sharp, clear central vision.
macular edema: The build-up of fluid in the macula caused by fluid leaking from blood vessels in the eye. It can blur and damage vision.
Magenblase syndrome: Swallowing too much air during a meal, causing excessive gas and discomfort. Also known as stomach bubble syndrome.
magnetic resonance imaging: A scan that creates detailed pictures of internal organs; commonly referred to as MRI. Magnetic resonance imaging uses radio waves, a strong magnetic field, and a computer to produce images of organs and internal tissues.
maintenance of wakefulness test: A test to measure sleepiness during the day. A tester measures how long it takes a person who is sitting up in a chair or bed to fall asleep after he or she has been asked to stay awake.
major depression: Depression that interferes with daily life for an extended period. Episodes of major depression during bereavement can be distinguished from normal sadness by such symptoms as persistent feelings of worthlessness, thoughts about death, feelings of guilt, persistent trouble functioning, and marked mental and physical sluggishness.
major histocompatibility complex molecule: Molecules that help protect the body from foreign substances. These molecules display proteins on the surface of cells so that protective immune system cells can kill the protein if it is harmful to the body.
maladaptive stress response: An unhealthy physiological response to stressors, in which the stress response often does not turn off even when the stressor disappears.
malaise: A general feeling of illness that can be a sign of disease.
malignant hypertension: A dangerous type of high blood pressure marked by an unusually sudden rise in blood pressure to very high levels, often accompanied by headache, blurred vision, and seizures.
malnutrition: Failure to eat or to properly absorb the nutrients needed for good health.
MAOIs: Abbreviation for monoamine oxidase inhibitors, medications used to treat depression. They work by making the chemical messengers serotonin and norepinephrine more available.
mast cell: A cell involved in allergic reactions. When stimulated, it releases chemicals like histamine that signal infection and cause inflammation.
mastoid bone: The bone in the skull behind the ear.
mastopexy: A cosmetic surgery to reshape and lift drooping breasts. Commonly known as a breast lift.
masturbation: Sexual self-stimulation.
maximizer: A person who typically evaluates all options before making a decision, in an effort to identify the perfect choice, and who never settles for second-best.
meal plan: A detailed guide outlining the amounts and types of food a person should eat each day.
Medicaid: A government program that offers health care for low-income Americans of any age.
Medicare: A government program that offers health care for Americans ages 65 and older.
Medigap insurance: Health insurance policies that fill in the holes in Medicare coverage.
medulla: Refers to the middle of something.
megaloblastic anemia: Fewer than normal healthy red blood cells in circulation, caused by a lack of folate or vitamin B12. Red cells become large and deformed, and are unable to carry oxygen efficiently.
meglitinides: A type of medication taken to treat type 2 diabetes.
melanin: A substance that gives the skin, hair, and eyes their natural color.
melanocytes: Cells located deep in the epidermis that produce melanin, the pigment that colors skin.
melanoma: The most dangerous type of skin cancer.
melatonin: A hormone that regulates the body's sleep-wake cycle.
membrane: A thin layer of tissue that surrounds or lines organs or cavities.
memory T cells and B cells: Immune cells that remember harmful agents that have entered the body in the past. When they spot the substance again, they spur the immune system to eliminate the invader.
Ménière's disease: An illness caused by a fluid imbalance in the inner ear.
meninges: The three membranes that cover and protect the brain and spinal cord.
meningitis: Swelling of the membranes that cover and protect the brain and spinal cord.
menopause: The point marking the end of menstruation, officially designated as one year after a woman's final period.
metabolic equivalents: Units used to estimate the oxygen consumption, or metabolic cost, of physical activity, and, hence, its intensity. One metabolic equivalent (MET) is the estimated energy cost of the body at rest.
metabolic syndrome: A cluster of risk factors that accelerate the progression of heart disease.
metabolism: The chemical reactions that occur in all living organisms to maintain life. An example is converting food into energy that the body needs to function.
metastasis: The spread of cancer cells from the primary site to another part of the body.
metered-dose inhaler: A device that delivers a specific dose of an inhaled asthma medication.
Methanobrevibacter smithii: Bacteria in the gut that help with the digestion of complex sugars.
METs: Abbreviation for metabolic equivalents, units used to estimate the oxygen consumption, or metabolic cost, of physical activity, and, hence, its intensity. One MET is the estimated energy cost of the body at rest.
MHC molecule: Abbreviation for major histocompatibility complex molecule, molecules that help protect the body from foreign substances. These molecules display proteins on the surface of cells so that protective immune system cells can kill the protein if it is harmful to the body.
microalbuminuria: Leakage of small amounts of a protein called albumin into the urine caused by kidney disease or damage.
microaneurysm: A tiny bulge that develops in the wall of a blood vessel.
microbe: A microorganism.
microdermabrasion: A cosmetic procedure in which tiny crystals under high pressure are sprayed on the face. This buffs away the outer layer of skin, eliminates fine lines, and improves the look of the skin.
microgram: A unit of mass, equal to one-thousandth of a milligram. Abbreviated as mcg.
micronized: Reducing a substance to very small particles.
micronutrients: Vitamins and minerals needed to maintain normal body functions and prevent certain illnesses.
microvascular disease: A condition in which the smallest blood vessels in the walls of the heart are narrowed or inelastic.
microvasculature: The body's small blood vessels.
micturition: Emptying the bladder. Also called urination or voiding.
middle ear: The air-filled cavity behind the eardrum that contains the three small bones that transmit sound vibrations to the inner ear.
migraine headache: A severe headache with pain that usually begins on one side of the head. Symptoms may include visual disturbances (called aura), nausea, vomiting, and sensitivity to light or noise.
migraine with aura: A severe headache preceded by visual disturbances such as flashing lights, seeing lines, or a blind spot.
migraine without aura: A severe headache that is not preceded by visual disturbances such as flashing lights. Also known as common migraine.
mild cognitive impairment: The loss of some brain functions, such as memory, thinking, or language, that is noticeable, but doesn't interfere with ability to carry out daily tasks.
milligram: A metric unit of weight equivalent to one-thousandth of a gram. Abbreviated as mg.
mindfulness: A practice with its roots in Buddhism that encourages people to be more fully aware of the present moment. Often achieved through meditation.
mindfulness meditation: A form of meditation with roots in ancient Buddhist practice through which a person has a calm awareness of his or her body and feelings and is fully engaged in the present; also called insight meditation.
mindfulness-based cognitive behavioral therapy: A well-established acceptance-based therapy, used principally in treatment of depression and anxiety.
mindlessness: Acting without full attention to one's surroundings, behavior, or internal experience.
miotic: An eye drop that constricts the pupil; used to treat glaucoma.
mitochondria: Small structures within cells that create break down nutrients and create energy for cells. Known as the power producers or energy factories of cells.
mitral valve: The valve that controls the one-way flow of blood from the left atrium to the left ventricle.
mitral valve prolapse: A valve problem in which one or both of the mitral valve flaps collapse backward into the left atrium. This may allow a small amount of blood to leak backward (regurgitate) through the valve.
mitral valve stenosis: A narrowing of the mitral valve opening that limits blood flow from the left atrium to the left ventricle.
monoamine oxidase inhibitors: Medications used to treat depression. They work by making the chemical messengers serotonin and norepinephrine more available.
monoclonal antibody: An antibody is a protein molecule that can bind to a virus and mark it for destruction by the immune system. A monoclonal antibody is a man-made substance used to treat some viral and other diseases.
monocytes: White blood cells that protect the body from disease by attacking and consuming foreign particles.
monounsaturated fat: A type of fat abundant in vegetable oils such as olive, peanut, sesame, and canola oils. Monounsaturated fats don't raise levels of unhealthy LDL cholesterol, and may even lower it.
Morton's neuroma: A thickening of nerve tissue between the toes that causes irritation, tingling, or a burning pain in the ball of the foot.
motilin: A hormone that helps the small intestine contract and move food through the digestive tract.
motility: The ability of the digestive tract to move its contents.
motor neuron: A nerve cell that directs activity in a specific group of muscle fibers.
motor unit: The pairing of a nerve cell and the group of muscle fibers it commands.
MRI: Abbreviation for magnetic resonance imaging--a scan that creates detailed pictures of internal organs. MRIs use radio waves, a strong magnetic field, and a computer to produce images of organs and internal tissues.
mucosa: Tissue that lines the tube-like structures of the body such as the respiratory and gastrointestinal tracts.
mucous cysts: Small cysts that form between the nail bed and the top joint of the finger.
mucous membrane: A thin layer that lines many cavities and structures in the body that are exposed to air in the environment, such as the nose, mouth, and lungs.
multi-infarct dementia: Memory loss and impaired thinking caused by tiny strokes that are often too small to notice until a sizable area of the brain is affected.
multinodular goiter: An enlargement of the thyroid gland with more than one lump or nodule appearing on the neck.
multiple sclerosis: An autoimmune disease in which the body's immune system mistakenly attacks myelin, the substance that covers nerve fibers.
multiple sleep latency test: A sleep test to measure daytime sleepiness. It times how quickly a person falls asleep when asked to rest in a quiet, darkened room during the day.
murmur: An sound heard during an examination of the heart caused by abnormal flow of blood through heart chambers or valves. Many heart murmurs do not indicate heart problems; others do.
muscle fatigue: Weakness felt in muscles when they have been tired out.
muscle fibers: Cells bundled together to make up muscle tissue. Also known as muscle cells.
muscle-contraction headache: A headache characterized by constant pressure, mild to moderate pain, and the feeling that a tight band is squeezing the head. Also known as a tension headache.
muscular endurance: The ability of muscle to continue to perform without stopping because of fatigue.
muscularis: The thin layer of smooth muscle lining of the colon or rectum.
musculoskeletal: Related to the muscles and the skeleton.
MUSE: Abbreviation for medicated urethral system for erection. In this therapy, a small drug pellet is inserted into the tip of the penis to produce an erection.
mutation: The process by which a change occurs in genetic material and is inherited by the next generation.
myalgia: Pain or tenderness in a muscle.
myasthenia: An abnormal weakness in a muscle or group of muscles.
mydriatic: A type of drug that widens the pupil.
myelin: A fatty material that surrounds and protects some nerve fibers.
myelography: A test that uses a special dye and X-rays to detect spinal cord problems. The dye is injected into the space surrounding the spinal cord, making the spinal cord, spinal canal, and nerve roots appear in detail on the X-ray.
myelopathy: A disorder in which the spinal cord is compressed, diseased, or damaged.
myocardial infarction: Medical term for heart attack, the sudden death of part of the heart muscle from lack of oxygen.
myocardial rupture: Tearing of one of the walls of the heart. It usually occurs immediately after a heart attack.
myocarditis: Inflammation of the heart muscle (myocardium).
myocardium: The middle layer of heart tissue. The muscular myocardium is sandwiched between the outer layer (epicardium) and the inner layer (endocardium).
myocyte: A muscle cell.
myofibrils: Long interlocking strands that make up muscle fibers.
myofilaments: The fundamental muscle proteins that form myofibrils. Myofilaments slide over one another, bunching up and generating force, when a muscle contracts.
myopia: Nearsightedness. An optical error in which light rays meet and focus before reaching the retina, making objects that are far away appear blurry.
myosin: A protein that helps muscle contract and relax.
nanograms per milliliter: A small quantity of a substance; equivalent to one-billionth of a gram (454 grams make 1 pound) in one-thousandth of a liter (1 liter is approximately 1 quart). Abbreviated as ng/ml.
narcolepsy: A sleep disorder that causes extreme sleepiness and uncontrollable sleep attacks, making a person fall asleep at inappropriate times during the day.
nasolabial folds: Lines in the skin leading from the nose to the outer corners of the mouth. Also known as smile or laugh lines.
natural killer cells: A type of white blood cell of the immune system. These cells destroy other cells that fail to display the right chemical flags signaling that they are normal cells.
natural recoverers: People who overcome addiction without treatment or formal self-help programs.
nebulizer: A device that converts a liquid medicine into a mist that can be breathed in.
necrosis: The premature death of living cells or tissues.
needle biopsy: Use of a hollow needle to remove a small sample of tissue for examination.
neoadjuvant therapy: A helper treatment given before a primary treatment is started, such as when chemotherapy is done before surgery in order to shrink a tumor.
neonatal: Relating to an infant younger than 4 weeks of age.
neoplasm: An abnormal growth of tissue, either cancerous or benign.
nephritis: Inflammation of the kidneys.
nephropathy: Kidney disease.
nerve block: Injection of a medication into one or more nerves to relieve pain.
nerve growth factor: A molecule in the body that promotes the growth and repair of nerve cells.
nerve sparing: When referring to prostatectomy, the surgical procedure that preserves the nerves needed to allow the penis to become erect.
neuralgia: A burning or stabbing pain that follows the path of a nerve.
neuritic plaques: Clumps of sticky proteins found in the brains of people with Alzheimer's disease.
neurofibrillary tangles: Twisted strands of proteins that are found inside the dead or dying nerve cells of people with Alzheimer's disease.
neuroleptic agents: Powerful tranquilizing drugs used to treat schizophrenia.
neurologist: A physician trained to diagnose and treat disorders of the nervous system, including the brain and spinal cord.
neuromuscular junction: The tiny space between the end of a nerve and the surface of a muscle.
neuron: A nerve cell.
neuropathy: Nerve damage and resulting loss of sensation, movement, or other function.
neuropeptides: Small proteins that aid in transmitting signals between nerve cells.
neurosyphilis: A rare infection of the brain or spinal cord that occurs when syphilis goes untreated for many years.
neurotransmitter: A chemical messenger released by nerve cells that transmits messages to nearby other nerve cells.
neurotransmitter receptors: Cell structures (usually proteins) that recognize specific neurotransmitters and bind to them. Once bound, a receptor often changes shape, causing a cascade of chemical events within the cell. These events can alter which genes are turned on or off and can make the cell more or less likely to release its neurotransmitters.
neutral alignment: Keeping the body in a straight line from head to toe except for the slight natural curves of the spine.
neutral posture: A standing or seated position in which the chin is parallel to the floor; the shoulders, hips, and knees are at even heights; and the knees and feet point straight ahead.
neutral spine: A position in which the back is straight except for the slight natural curves of the spine.
neutropenia: An abnormally low number of white blood cells.
neutrophils: White blood cells that seek out and engulf foreign cells.
nitrates: Medications that widen blood vessels; usually used to treat chest pain from angina and other heart problems.
nitric oxide: A compound produced by the endothelium (the lining of the interior walls of arteries) that helps widen blood vessels and counteract high blood pressure. Also called endothelium-derived relaxing factor.
nitroglycerin: A drug that relaxes blood vessels and increases the supply of blood and oxygen to the heart while reducing its workload. It is commonly used to treat angina.
NK: Abbreviation for natural killer cells, a type of white blood cell of the immune system. These cells destroy other cells that fail to display the right chemical flags signaling that they are normal cells.
NMDA receptor: Abbreviation for the N-methyl-D-aspartame receptor, a molecule on the surface of a brain cell that admits calcium when activated by the chemical messenger glutamate.
N-methyl-D-aspartame receptor: A molecule on the surface of a brain cell that admits calcium when activated by the chemical messenger glutamate.
NO: Abbreviation for nitric oxide, a compound produced by the endothelium (the lining of the interior walls of arteries) that helps widen blood vessels and counteract high blood pressure. Also called endothelium-derived relaxing factor.
nociceptors: Nerve endings that detect pain and transmit pain information to the brain and spinal cord.
nocturia: Waking up more than once during the night to urinate.
nodule: A small rounded bump or knot of tissue.
nomogram: A chart or graph of mathematical calculations of risk; used in making treatment recommendations and predicting outcomes.
non-HDL cholesterol: The sum of all cholesterol types other than high-density lipoprotein (HDL). These include very-low-density lipoprotein, low-density lipoprotein, and intermediate-density lipoprotein.
non-insulin-dependent diabetes: Now called type 2 diabetes. A disease in which levels of blood sugar (glucose) are too high initially because cells can't properly use insulin (a hormone that helps cells absorb glucose from the bloodstream). Over time the production of insulin may decline.
noninvasive test: A test that does not require any medical instruments to break the skin or enter the body.
nonketotic hyperglycemic hyperosmolar syndrome: A rare and very serious condition associated with type 2 diabetes. Symptoms include extremely high (more than 800 mg/dl) blood sugar levels, severe dehydration, and changes in mental status, ultimately resulting in coma.
nonproliferative retinopathy: A condition in which the walls of the small blood vessels in the retina leak serum and tiny pockets of swelling form in the walls of blood vessels. Also called background retinopathy.
non-REM sleep: The sleep phase that includes deep sleep, the type considered most important for preventing daytime sleepiness.
nonsteroidal anti-inflammatory drug: A drug that reduces swelling and pain.
noradrenaline: A hormone produced by adrenal glands that puts the body on heightened alert when a threat is perceived (the fight-or-flight response). Also known as norepinephrine.
norepinephrine: A hormone produced by adrenal glands that puts the body on heightened alert when a threat is perceived (the fight-or-flight response). Also known as noradrenaline.
normal-pressure hydrocephalus: A buildup of fluid in the brain that causes the brain to swell, and leads to slowing of mental function, trouble walking, and a loss of bladder control.
NSAID: Abbreviation for nonsteroidal anti-inflammatory drug, a drug that reduce swelling and pain.
nuclear tests: Tests that use tiny amounts of short-lived radioactive substances that can target particular organs or cell receptors to diagnose disease.
nucleus accumbens: Part of the brain's reward pathway that is most tightly and consistently responsive to pleasure. Also known as the pleasure center.
nucleus pulposus: The gel-like shock-absorbing central portion of each spinal disc.
nutraceutical: Dietary supplement containing concentrated forms of a presumed bioactive substance originally derived from food and used to enhance health in dosages exceeding those normally obtainable from food.
nutrients: Substances in foods that the body needs to survive.
obesity: A body weight that is much higher than is healthy. Defined as having a body mass index of 30 or more. Obesity puts a person at greater risk of developing numerous chronic diseases.
object of addiction: The psychoactive drug or rewarding behavior with which a person with addiction has a pathological relationship.
obstructive sleep apnea: A disorder marked by heavy snoring and interrupted breathing during sleep. It increases the risk of developing high blood pressure and having a stroke and is more common in people who are obese.
occipital lobe: The region in the back of the brain responsible for visual processing.
occlusion: The closing or blocking of a hollow organ or body part.
occult: Something not visible to the naked eye but seen under a microscope or through lab tests.
omega-3 fatty acids: Beneficial fats, also known as n-3 fatty acids. These are polyunsaturated fat found in fatty fish, such as salmon.
omega-6 fatty acids: Fatty acids found in certain foods that the body needs for good health but can't make on its own. Also known as n-6 fatty acids.
oncogene: A gene that, under certain conditions, can cause cancer.
oncologist: A physician who deals with the diagnosis and treatment of cancer. There are three types—medical oncologists, radiation oncologists, and surgical oncologists.
Ondine's curse: A rare and potentially fatal disorder in which a person may stop breathing, especially at night. Also called congenital central hypoventilation syndrome.
onychomycosis: Toenail fungus.
open prostatectomy: A surgical procedure in which an enlarged prostate is removed through an incision in the abdomen.
ophthalmologist: A physician who specializes in treating the eye and eye disease.
ophthalmoscope: An instrument with a light and mirrors for examining the deep interior of the eye.
opiate: Any painkilling drug such as morphine or codeine derived from the opium poppy.
opioid: Any narcotic, natural or synthetic, that behaves in the body like an opium-derived drug.
optic disk: The front surface of the optic nerve, where all the retinal nerve fibers come together to carry an image to the brain.
optic nerve: A cable of specialized nerve fibers that transmit visual impulses from the eye to the brain.
optician: A technician who helps select and fit eyeglasses or contact lenses for people with vision problems.
optimism: A characteristic frame of mind that leads a person to expect positive outcomes and to view the world as a positive place.
optometrist: A health care professional licensed to examine the eye, and diagnose and treat some eye diseases.
oral glucose tolerance test: A test to check for diabetes. It involves fasting overnight and having blood sugar levels checked before and after drinking a sugary solution.
oral mucosa: The layer of soft pinkish tissue that lines the interior of the mouth.
orbit: The bony socket that holds the eyeball.
orbital irradiation: X-ray treatment to the eye; sometimes used in more serious cases of Graves' eye disease.
orchiectomy: Surgery to remove the testicles. Usually done to remove a cancerous testicle or to lower testosterone levels and slow or halt the growth of prostate cancer.
organic matrix: The protein framework of bone tissue.
organonitrile: A chemical found in cruciferous vegetables that may have anti-cancer properties.
orgasm: The series of pleasurable, rhythmic muscle contractions that mark the peak of sexual arousal and the release of muscle tension.
orthopedist: A medical doctor who specializes in correcting disorders of the bones, joints, muscles, and tendons.
orthosis: A custom shoe insert that helps cushion or realign the foot.
orthostatic hypotension: A sudden drop in blood pressure upon standing or getting out of bed, causing dizziness.
osseointegration: A process in which bone heals around an implant to create a stable anchor.
ossicles: Three bones in the middle ear that move in response to sound vibrations.
ossification: The process by which bone is formed.
osteoarthritis: A joint disease in which the cartilage that lines the joints slowly deteriorates. Also called degenerative joint disease.
osteoblasts: Cells that build bone tissue.
osteoclasts: Cells that remove bone tissue.
osteocytes: A cell that is embedded in fully formed bone.
osteomalacia: A condition in which bones are soft and weak, usually due to a lack of vitamin D or an inability of the body to use vitamin D properly.
osteomyelitis: A bone infection caused by bacteria or fungi.
osteons: The building blocks of compact bone, the hard, tightly-packed tissue that forms the outer shell of bones.
osteopath: A doctor licensed to practice medicine, perform surgery, and prescribe drugs. The training is similar to that of a regular M.D., but more emphasis is placed on the importance of the musculoskeletal system and the body's ability to heal itself.
osteopenia: Mild thinning and weakening of the bones; bone density is lower than normal but not low enough to be classified as osteoporosis.
osteophyte: An outgrowth of bone on a joint or spinal disk; commonly called a bone spur.
osteoporosis: Significant thinning and weakening of bones over time, making them vulnerable to breaks.
osteotomy: An operation in which bone is cut to change its alignment or shorten or lengthen it.
otic capsule: The bony shell that surrounds the inner ear.
otitis externa: An infection of the skin lining the ear canal of the outer ear. Also called swimmer's ear.
otitis media: An infection of the middle ear.
otosclerosis: An abnormal bony growth in the middle ear that causes hearing loss.
outbreak: Synonymous with epidemic. Sometimes used to refer to a local epidemic as compared to a larger, general epidemic.
outer ear: The external part of the ear, as well as the external ear canal and the eardrum.
outpatient: A person who receives treatment at a hospital or other medical facility but does not stay overnight.
output: The loudest sound that a hearing aid can produce.
ovariectomy: Surgical removal of one or both ovaries.
overactive bladder: Frequent urination and urges to urinate.
overt proteinuria: A condition of declining kidney function. It is part of the progression of kidney disease, developing after microalbuminuria (when a damaged kidney begins to leak small amounts of a protein called albumin into urine) and before chronic kidney disease.
overweight: A body weight above the healthy range but not obese. Usually defined as a body mass index of 25 to 29.9.
ovulation: The release of a mature egg from the ovary, at which time it is available to be fertilized by sperm.
oxidant: An unstable molecule in the body that plays a role in aging and can damage tissue. Also known as a free radical.
oxidation: A process in which oxygen combines with a substance, altering its structure and changing or destroying its normal function.
oxygenated blood: Blood that has moved through the lungs where it has absorbed oxygen; oxygenated blood moves from the lungs into the heart, from which it is then pumped throughout the body.
pacemaker, artificial: A small electronic device generally placed in the chest to correct an irregular heartbeat. It generates small electrical pulses that prompt the heart to beat at a normal pace.
pacemaker, natural: A specialized cluster of cells called the sinoatrial node in the top of the right atrium. The pacemaker produces a steady flow of beat now signals that flash across the atria and then pass through the atrioventricular node to the ventricles.
PAD: Abbreviation for peripheral artery disease, a condition caused by atherosclerosis in the arteries in the legs or leading to them.
painkillers: Drugs that relieve pain.
palate: The tissues that make up the roof of the mouth.
palliative care: Treatment that relieves the symptoms of a serious illness, but does not cure the disease itself.
palpate: To examine a part of the body by touching it carefully.
palpitation: Sensation that the heart is beating rapidly or irregularly.
palsy: Paralysis in part of the body, often with loss of sensation and uncontrolled body movements.
pancreas: A gland in the abdomen that produces digestive enzymes and hormones.
pandemic: A disease outbreak affecting large populations or a whole region, country, or continent.
pannus: An abnormal layer of tissue that forms over joints or the cornea of the eye.
papillary muscles: Threads of muscle that pull the heart valves between the upper and lower chambers of the heart closed during heart contractions.
paraplegia: Paralysis of the legs and lower part of the body.
parasomnias: Sleep disorders, such as night terrors or sleep walking, that periodically interfere with sleep.
parasympathetic nervous system: Part of the nervous system that calms body systems excited by the stress hormones.
parathyroid glands: Glands responsible for releasing a hormone that controls calcium levels and influences bone loss and growth.
parathyroid hormone: A hormone that controls levels of calcium and phosphorous in the blood and influences bone loss and growth.
parietal lobe: Part of the brain. It plays a role in sensory processes, like pain and touch, and language.
Parkinson's disease: A brain disorder that causes movement problems, including shaking, difficulty walking, and rigidity in muscles.
paroxysm: A sudden, violent attack or convulsion; or the worsening of symptoms or recurrence of disease.
paroxysmal hemicrania: A rare form of headache. Sufferers experience a severe throbbing, drilling pain on one side of the face or behind the eye.
passive immunity: Immunity that is conferred by another, such as a mother's antibodies protecting her baby during gestation and shortly after birth.
patch test: A test used to diagnose whether a rash was caused by a reaction to certain allergens, such as poison ivy or a cosmetic ingredient, or an irritant such as soap.
patella: The thick bone that protects the knee joint; also known as the kneecap.
pathogen: A tiny organism such as a virus, bacterium, or parasite that can invade the body and produce disease.
pathology: The underlying abnormalities that contribute to or are characteristic of a disease.
patient-controlled analgesia: A method that allows a person to control, within limits, the amount and timing of pain medication he or she receives. It is usually done by pressing a button to release the medication from a computerized pump into an IV.
pattern-recognition receptors: Proteins that recognize classes of pathogens and stimulate the innate immune system to signal the adaptive immune system.
PCOS: Abbreviation for polycystic ovary syndrome, an inherited disorder characterized by the formation of abnormal cysts in enlarged ovaries; a leading cause of female infertility and a common cause of excess facial or body hair (hirsutism).
PDE5 inhibitors: Abbreviation for phosphodiesterase type 5 inhibitors, drugs that can help a man achieve and maintain an erection.
peak bone mass: The greatest amount of bone tissue that a person has during his or her life.
peak flow: A measure of how fast a person can blow air out of the lungs.
peak flow meter: A device to assess lung function, often used to diagnose and monitor asthma.
Pediculus humanus capitis: A blood-sucking parasite commonly known as the louse (plural, lice) that can cause an itchy scalp; infestations are highly contagious and especially common in school-age children.
pellagra: A rare disease brought on by severe niacin deficiency that causes diarrhea, dermatitis, and dementia.
pelvic floor: The sling of muscles that support the intestines and bladder, as well as the uterus in women. Weak or damaged pelvic floor muscles can cause incontinence or diminished sexual pleasure, among other problems.
penile prosthesis: An inflatable or bendable device that is implanted in the penis to allow a man with erectile dysfunction to have erections when he wishes.
pepsin: Enzymes secreted by the stomach to break down protein.
peptic ulcer: A raw, crater-like sore in the lining of the stomach or duodenum that causes burning stomach pain.
percutaneous diskectomy: Surgical removal of part of a spinal disk that is bulging out abnormally and pressing on a nerve root or the spinal column.
percutaneous electrical nerve stimulation: A pain relief therapy that uses needles to deliver low-voltage electrical current under the skin to stop pain signals from reaching the brain.
percutaneous transluminal coronary angioplasty: A procedure used to open blocked coronary arteries. A small, thin tube with a tiny balloon at its tip is inserted into a narrowed coronary artery. The balloon is then inflated to widen the narrowed area. A stent may be put in place to hold the artery open. Percutaneous transluminal coronary angioplasty is also known as balloon angioplasty.
perforation: A hole, such as an ulcer, in an organ or tissue.
performance anxiety: Concern about sexual performance that is so severe that it leads to sexual dysfunction.
perfusion: Passage of a fluid through a specific organ or an area of the body.
perfusion defect: A test result that indicates abnormal blood flow or areas of damaged or dead heart muscle.
pericarditis: Inflammation of the pericardium, the heart's sac-like covering.
pericardium: The fibrous sac that surrounds the heart and the roots of the major blood vessels.
perimenopause: The transition time in a woman's life that begins when ovaries produce less estrogen and menstruation becomes less frequent, and ends when the ovaries no longer produce eggs and menstruation stops.
perineum: The area of skin between the vagina and anus in women, and between the scrotum and anus in men.
periodic limb movement disorder: A sleep disorder in which the legs jerk or cramp repeatedly during the sleep.
periodization: An exercise strategy that varies reps, sets, and resistance to alternate heavier and lighter workouts over a period of time.
periodontal disease: Diseases, including gingivitis and periodontitis, that attack the gum tissue and the structures supporting the teeth. Also called gum disease.
periodontitis: An advanced stage of gum disease that attacks the teeth's supporting structures.
peripheral artery disease: A condition caused by atherosclerosis in the arteries in the legs or leading to them.
peripheral nervous system: The parts of the nervous system outside of the brain, brain stem, and spinal cord.
peripheral neuropathy: Damage to the long nerves radiating from the spine to the arms and legs.
peripheral vascular disease: Narrowing of blood vessels that supply blood to the legs, arms, stomach, or kidneys.
peripheral vision: Side vision, or what the eye perceives outside the direct line of vision.
peristalsis: Wavelike movement of intestinal muscles that propels food through the digestive tract.
peritoneal dialysis: Treatment for kidney failure that uses a machine to remove toxins from the bloodstream.
peritonitis: Inflammation of the membrane that line the abdominal cavity and surrounds most abdominal organs.
pernicious anemia: A form of anemia in which red blood cells enlarge and decrease in size due to an inability to properly absorb vitamin B12.
personal emergency response system: A device worn around the neck or wrist that allows a person to call for help by pressing a button.
pessary: A device placed in the vagina to support or correct the position of the uterus, rectum, or bladder.
pessimism: A characteristic frame of mind that leads a person to expect negative outcomes and to view the world as a negative or fearful place.
petechiae: Pinpoint-sized red or purple spots that appear in clusters on the skin, caused by bleeding under the skin.
PET scan: Abbreviation for positron emission tomography, a medical imaging test that uses a radioactive substance to assess organ and tissue function in the body and to look for disease.
Peyronie's disease: Scarring of some of the tissue inside the penis, causing the penis to bend at an angle during an erection.
pH monitoring: A test to determine whether stomach acid is backing up into the esophagus. For this test, a sensing probe is inserted through the nose and positioned above the lower esophageal sphincter.
phacoemulsification: A method of cataract removal. It uses ultrasound waves to break up the clouded lens of the eye so it can be suctioned out with a needle.
phagocytes: Cells that can ingest other cells, bacteria, and foreign particles.
phase shift disorder: Sleep problem that results when a person's internal clock becomes out of sync with external time. This can be a problem for people who work the night shift.
phase-2 enzyme: A helpful enzyme that seems to clear toxins and help prevent cancer-causing substances from binding to DNA.
phenothiazines: Powerful tranquilizing drugs used to treat schizophrenia and, sometimes, severe nausea.
phenylpropanolamine: A decongestant drug used to treat nasal congestion and sometimes mild incontinence.
pheochromocytoma: A rare adrenal gland tumor that secretes hormones that narrow blood vessels and increase blood pressure.
phlegm: Thick, sticky mucus secreted by mucous membranes, such as the sinuses.
phonophobia: Sensitivity to noise, often experienced during a migraine attack.
phosphodiesterase type 5: An enzyme that breaks down substances that help the penis become erect and maintain an erection.
photocoagulation: Use of a laser to seal off blood vessels.
photodynamic therapy: A medical treatment that uses a light source to activate a photosensitizing drug (one that becomes activated by light exposure). Often used in oncology, dermatology, and cosmetic surgery.
photophobia: Sensitivity to light, often experienced during a migraine attack.
photopsia: A sensation of sparks or flashes of light across the visual field.
photorefractive keratectomy: Laser surgery used to reshape the cornea in order to correct vision problems.
photorejuvenation: A cosmetic procedure that uses intense pulsed light to remove wrinkles and improve skin tone and texture.
physiatrist: A physician who specializes in physical medicine, pain, and rehabilitation. These doctors diagnose and treat sports injuries and degenerative conditions like arthritis or low back pain, and oversee rehab for patients with severe impairments resulting from trauma, stroke, and other conditions.
physical activity: Any voluntary body movements that burn calories, including walking up stairs, vacuuming a floor, going for a brisk stroll, or engaging in a structured program of exercise.
physical dependence: The process through which the body becomes accustomed to a psychoactive drug or rewarding behavior and misses it if it's taken away. People with physical dependence who stop or cut down on their substance or activity of choice might develop uncomfortable withdrawal symptoms.
physical fitness: A state of being physically sound and healthy; having the ability to perform physical activity well.
phytochemicals: Substances made by plants that have biological effects in the human body. Examples include isoflavones, lycopene, lutein, and zeaxanthin.
phytoestrogen: A plant component that mimics the effects of estrogen hormones in the body.
Pick's disease: A brain disorder that causes dementia, neurotic behavior, and gradual changes in personality and emotional control.
pineal gland: A gland located in the middle of the brain, between the brain's two hemispheres, that produces melatonin in response to declining light.
Pittsburgh Compound B: A substance that binds to amyloid proteins in the brain (markers for Alzheimer's disease), making them visible under positron emission tomography (PET) scanning.
pituitary gland: The so-called master gland, located at the base of the brain. It controls and regulates the thyroid and other glands throughout the endocrine system.
placebo: A false or inactive medication or treatment that may still offer relief despite being ineffective. In clinical trials, the effectiveness of a new drug is often tested against a placebo.
placebo effect: A change or improvement in symptoms that is due to a dummy medication or treatment (placebo) rather than a real drug or treatment.
plantar fascia: Connective tissue in the foot which joins the heel bone to the ball of the foot.
plantar fasciitis: An inflammation of the plantar fascia; the leading cause of heel pain.
plantar wart: A wart on the sole of the foot, caused by a virus.
plaque: 1) A layer of bacteria that forms on the surface of a tooth and can cause dental disease. 2) A fatty deposit in or on the walls of an artery, as part of atherosclerosis.
plasma: The fluid in which blood cells are suspended.
plasma cells: White blood cells that produce large quantities of antibodies as part of an immune system response.
plasmin: An enzyme that breaks down the protein involved in clotting blood (fibrin), dissolving the clot.
platelet: A colorless, disk-shaped cell in the blood that is necessary for clotting.
podiatrist: A physician who specializes in the medical, surgical, and orthopedic management of foot and ankle disorders.
poliosis: A localized patch of gray or white hair on the scalp, eyebrows, or eyelashes.
polycystic ovary syndrome: An inherited disorder characterized by the formation of abnormal cysts in enlarged ovaries; a leading cause of female infertility and a common cause of hirsutism.
polydipsia: Excessive thirst.
polymyositis: A rare disease in which the muscles become inflamed and weak.
polyp: An abnormal, noncancerous growth that protrudes from mucous membranes, like those found in the sinuses and colon lining.
polysomnography: A sleep study that examines brain waves and other measures of physiological functioning.
polyunsaturated fat: A type of fat that is abundant in soybean, corn, cottonseed, safflower, and sunflower oils, as well as in fatty fish. One type, omega-3 fats, are especially important for cardiovascular health.
polyuria: Excessive urination.
positive psychology: A branch of psychology that studies mental health rather than illness, focusing on how life can be more happy and fulfilling.
positron emission tomography: A medical imaging test that uses a radioactive substance to assess organ and tissue function in the body and to look for disease. Commonly called a PET scan.
posterior chamber: The part of the eye behind the iris and in front of the lens that is filled with aqueous humor.
posterior heel bursitis: An inflammation of the bursa sac surrounding the joint in the heel of the foot, causing swelling and pain.
posterior keyhole foraminotomy: A minimally invasive surgical procedure that is sometimes an option for repairing a herniated disk.
posterior myocardial infarction: Heart attack involving the rear wall of the heart muscle.
postherpetic neuralgia: Nerve pain caused by the herpes zoster virus, also known as shingles.
postmenopausal osteoporosis: Bone loss caused by lower estrogen levels associated with menopause. Sometimes called type I osteoporosis.
postmenopause: The period in a woman's life lasting from the end of perimenopause until the end of life.
postpartum: Pertaining to the period after giving birth.
post-traumatic headache: A persistent headache resulting from a head or neck injury, sometimes lasting for a year or more.
post-traumatic stress disorder: A prolonged reaction to a traumatic event. Post-traumatic stress disorder can cause crippling anxiety and leading to other problems, such as sleep disturbances, depression, and substance abuse. Often referred to as PTSD.
post-void residual: The amount of urine left in the bladder after urinating.
power: Force times speed of movement. It reflects how quickly a given force is exerted.
power training: An emerging field of physical medicine aimed at boosting the ability to exert strength quickly, especially in relation to practical, day-to-day tasks.
prazosin: A member of a class of drugs called alpha blockers. Prazosin eases the symptoms of benign prostatic hyperplasia by relaxing smooth muscle tissue in the capsule that surrounds the prostate.
precursor: A substance that the body can convert into the active form of a vitamin. One example is beta carotene, which the body can convert into vitamin A as needed.
prediabetes: A fasting blood sugar level above a healthy level, but still below the level used to diagnose diabetes. An individual with prediabetes is at increased risk for developing diabetes.
preeclampsia: High blood pressure during pregnancy accompanied by such signs as protein in the urine and swelling of the hands and feet; can progress to eclampsia, characterized by seizures.
prehypertension: Blood pressure that is above normal but not high enough to qualify as hypertension. An individual with prehypertension is at increased risk for developing hypertension.
preload reduction: A method of reducing cardiac workload by decreasing the pressure of blood entering the heart.
premature atrial contraction: An early beat in an atria that feels like the heart skipped a beat.
premature ejaculation: Ejaculation that occurs before or immediately after penetration; this can interfere with a couple having a mutually satisfying sexual experience.
premature ventricular contraction: An early beat in a ventricle that feels like the heart skipped a beat.
presbycusis: Age-related hearing loss caused by the death of hair cells in the inner ear.
presbyopia: Age-related difficulty focusing the eyes at close range, as the flexible lens of the eye becomes less elastic.
priapism: An erection that lasts longer than three hours. Emergency medical treatment is required to prevent permanent damage to the penis.
prick test: A commonly used skin test to confirm hypersensitivity to a broad range of allergens.
primary angioplasty: Use of angioplasty as the first treatment to open a blocked artery that is causing a heart attack, rather than using clot-busting (thrombolytic) drugs.
primary hypertension: High blood pressure with no known cause. Also known as essential hypertension.
primary osteoporosis: Bone loss that results from a normal physiological process, such as menopause or aging.
prion: The smallest known infectious agent; unlike a virus or bacterium it is made entirely of protein and contains no nucleic acid or chromosomes.
probate: A public, legal process supervised by the courts after a person dies that helps ensure debts are paid and assets are properly owned and correctly distributed.
probiotic: Live microorganisms used to benefit health, such as the L. acidophilus bacteria found in yogurt.
procedural memory: The long-term memory of skills and procedures, or how-to knowledge. Also called implicit memory.
processes: Bony projections that extend in several directions from each vertebra bone in the spine.
prodrome: A group of early symptoms preceding a given disease or condition. For example, a migraine prodrome (fatigue, hunger, nervousness) may occur hours or days before the headache strikes.
progesterone: A female steroid hormone produced by the ovaries that prepares the uterine lining for pregnancy.
progestin: A synthetic compound that produces effects similar to those of the hormone progesterone.
progestogen: Any hormone having the same effect as progesterone in the body; refers to both natural progesterone and synthetic progestin.
prognosis: A prediction on how a person's disease will progress in the future.
progressive muscle relaxation: A mind/body technique for inducing the relaxation response that involves isolating, tensing, and relaxing specific sets of muscles in sequence.
prolapse: A condition in which an organ or other body part drops from its normal position.
prolapsed disk: When part of a spinal disk bulges out of a tear or weak spot in the disk's tough outer shell. Also known as herniated disk.
proliferative retinopathy: An advanced stage of diabetic eye disease characterized by the development of new blood vessels that grow into the vitreous cavity; they are fragile and may bleed and cause loss of vision.
prophylaxis: Steps taken to prevent a particular disease or condition, such as taking nitroglycerin to prevent angina.
proprioception: The ability to sense the position of one's body in space, in relation to other objects.
proptosis: Forward bulging or displacement of an organ, especially of an eye. See exophthalmos.
prospective study: A type of research method that collects data on a group of people at the start of the study and then follows them into the future, gathering data over time.
prostaglandins: A group of chemicals that have hormone-like actions; prostaglandins help regulate blood pressure and contraction of smooth-muscle cells (for example, those in the lining of the blood vessels).
prostate cancer: Cancer of the prostate gland.
prostate gland: A walnut-shaped gland at the base of the male bladder. It produces a fluid that forms part of semen.
prostate-specific antigen: A protein produced by the prostate. Elevated levels may indicate the presence of cancer, benign prostatic hyperplasia, or prostatitis. Often referred to as PSA.
prostatic carcinoma: Another name for prostate cancer.
prostatic urethral stent: A small, springlike cylinder, designed to relieve pressure from an enlarged prostate and improve urine flow by widening a narrowed urethra.
prostatism: A blockage at the base of the bladder that reduces or prevents the flow of urine into the urethra, the tube that carries urine out of the body (also known as bladder outlet obstruction). Typical symptoms include feeling the need to urinate right away yet having to strain to do so, having a weak urinary stream, dribbling after urinating, feeling as though the bladder has not been emptied completely, needing to urinate frequently, or experiencing urinary incontinence.
prostatitis: An inflammation of the prostate gland, sometimes caused by a bacterial infection, which may result in painful or difficult urination.
prosthesis: An artificial device such as a hearing aid, artificial joint, or dentures that substitutes for a missing body part.
protease inhibitor: A class of drugs that help fight retrovirus infections; commonly prescribed to treat human immunodeficiency virus (HIV).
protein: One of the three major nutrients (along with carbohydrates and fats). It is used by the body for building and repairing tissues. Protein is derived primarily from animal sources but can be obtained from nuts and seed, some grains, and other plant sources.
protocol: A plan that lays out the procedures that will be followed in conducting a physical examination, a research study, or the treatment of a disease.
PSA: Abbreviation for prostate-specific antigen, a protein produced by the prostate. Elevated levels may indicate the presence of cancer, benign prostatic hyperplasia, or prostatitis.
PSA velocity: The rate at which a man's PSA level increases over time.
pseudoephedrine: A decongestant drug that may also relieve mild incontinence.
pseudogout: Arthritis caused by crystals of calcium pyrophosphate dihydrate in the joints. Also known as calcium pyrophosphate dihydrate disease.
psoriasis: A common skin disease characterized by thickened patches of inflamed red skin; sometimes accompanied by painful joint swelling and stiffness.
psychodynamic therapy: A form of therapy that focuses on how life events, desires, and close relationships lead to conflict, symptoms such as anxiety or depression, and difficulty in managing life's tasks.
psychogenic: Symptoms and illnesses that have a psychological cause, rather than a physical one.
psychogenic erectile dysfunction: Difficulty in getting or maintaining erections because of a psychological cause, such as stress or depression.
psychosomatic: Symptoms and illnesses that involve both the mind and the body, in which psychological stress may result in physical illness.
PTCA: Abbreviation for percutaneous transluminal coronary angioplasty, a procedure used to open blocked coronary arteries.
ptosis: A drooping of the eyelid attributed to weakened muscles.
PTSD: Abbreviation for post-traumatic stress disorder, a prolonged reaction to a traumatic event. PTSD can cause crippling anxiety and leading to other problems, such as sleep disturbances, depression, and substance abuse.
puborectalis muscle: A pelvic floor muscle that forms a sling around the rectum and helps maintain fecal continence.
pudendal arteries: Arteries supplying blood to the genital area.
pudendal nerve: The nerve that carries sensation from the genital area to the central nervous system.
pulmonary: Pertaining to the lungs.
pulmonary edema: A condition caused by excess fluid accumulating in the lungs, making breathing difficult.
pulmonary embolism: Blockage of one or more arteries in the lungs by a blood clot that formed elsewhere, often in the legs. Typically accompanied by sudden shortness of breath, chest pain, and cough.
pulmonary veins: The veins that carry blood from the lungs to the left atrium.
pulp: Tissue containing nerves and blood vessels that fills the chamber at the center of the tooth.
pulse pressure: The difference between systolic blood pressure and diastolic blood pressure (systolic pressure minus diastolic pressure = pulse pressure). Pulse pressure may help predict heart disease risk.
pump failure: When the heart muscle becomes so weak that it can no longer pump enough blood to the rest of the body.
pupil: The dark, circular opening in the middle of the iris of the eye.
purulent: Formed of or containing pus.
pus: A thick, yellow or green liquid that is composed of dead cells and bacteria, most often found at the site of a bacterial infection.
pyloric sphincter: A muscular valve at the lower end of the stomach that opens to the duodenum.
pyridoxine: A form of vitamin B6.
quadriplegia: Paralysis of all limbs, often caused by a severe neck injury.
quantitative computed tomography: A modification of computed tomography that provides measurements of bone mass as well as an image.
quarantine: A period of time in which a sick person is kept away from others to prevent the spread of disease.
quick relievers: Medications that quickly open the bronchial tubes by relaxing the muscles surrounding these airways.
quiet sleep: Any sleep other than REM sleep, in which thinking and most physiological activities slow, but movement still occurs. Also called non-REM sleep.
radial tunnel syndrome: A condition in which the radial nerve is compressed at the elbow, causing pain, numbness, tingling, and muscle weakness in the hand and arm.
radiation: Energy in the form of particles or waves, such as x-rays and gamma rays. Radiation is often used to help make a diagnosis, as in x-rays, or as a treatment for cancer.
radiation therapy: Treatment with high-energy rays (from x-rays or other sources) designed to control disease and destroy cancer cells.
radical prostatectomy: Surgery to remove the entire prostate.
radiculopathy: Pain caused by irritation of a nerve as it exits the spinal cord.
radioactive iodine: A radioactive form of iodine that can be used as a tracer during a radioactive iodine uptake test or a radioactive thyroid scan. Much larger amounts are used in the treatment of hyperthyroidism.
radioallergosorbent test: A blood test used for identifying allergens.
radiofrequency: A non-surgical technique using an electromagnetic current to penetrate deep into the body's tissues, which can be used to treat pain, cancer, and heart rhythm disorders, among other conditions.
radiograph: Another name for an x-ray.
radionuclide imaging or scan: Another name for nuclear tests: tests that use tiny amounts of short-lived radioactive substances that can target particular organs or cell receptors to diagnose disease.
radionuclides: Short-lived radioactive chemicals that are used in nuclear imaging tests.
rales: Abnormal lung sounds that might be a sign of fluid buildup congestion in the lungs.
randomized: A feature of many clinical trials in which participants are randomly assigned to either a group to be tested or a control group.
randomized controlled trial: A study in which researchers choose a study population at random; one group receives the intervention (such as a nutritional supplement) and another group receives a placebo. Often referred to as an RCT.
range of motion: The extent of movement—and thus flexibility—in a joint, measured in the degrees of a circle.
rapid eye movement sleep: A period of intense brain activity during sleep, often associated with dreams; named for the rapid eye movements that occur during this time. Also called dreaming sleep.
RAST: Abbreviation for radioallergosorbent test, a blood test used for identifying allergens.
Raynaud's syndrome: A condition in which the blood vessels in the fingers and other extremities narrow in response to cold or stress, causing them to turn white or blue.
RCT: Abbreviation for randomized controlled trial, a study in which researchers choose a study population at random; one group receives the intervention (such as a nutritional supplement) and another group receives a placebo.
RDA: Abbreviation for recommended dietary allowance, the average daily amount of a nutrient that will meet the nutritional needs of almost all (97%–98%) healthy people at specific stages of their lives.
reactive arthritis: Joint problems triggered by bacterial or viral infection elsewhere in the body.
rebound insomnia: Insomnia caused by withdrawal from sleep medication; usually it is at least as serious as before the medication was used.
receptors: Structures on the outside of a cell membrane that permit attachment of specific chemicals.
recessive: A gene that will not be expressed in the offspring unless it is inherited from both the mother and father. A recessive gene from one parent that is paired with a dominant gene from the other parent will be overridden by the dominant gene.
recombinant tissue plasminogen activator: A thrombolytic (clot-dissolving) drug made using recombinant DNA technology; used to dissolve blood clots causing an ischemic stroke, pulmonary embolism, or myocardial infarction.
recommended dietary allowance: The average daily amount of a nutrient that will meet the nutritional needs of almost all (97%–98%) healthy people at specific stages of their lives.
recovery: A process of overcoming addiction to alcohol, other psychoactive substance, or addictive behavior. Often this involves a commitment to abstinence, but sometimes it involves reduced use rather than complete abstinence.
rectocele: A weakening of the vaginal wall that allows the rectum to bulge into the vagina.
rectum: The last 12 centimeters of the colon, through which waste is eliminated from the body.
refraction: The deflection of light as it passes through one medium to another of different density; also refers an eye test to evaluate the eye's ability to focus.
regurgitation: Leakage of blood back into a heart chamber that occurs when a heart valve doesn't close properly
rehabilitative driving specialist: A professional trained to evaluate driving skills and, when appropriate, suggest equipment and adaptations to make driving safer for people with certain physical or mental limitations.
rejection: A reaction that occurs when a person's immune system recognizes a transplanted organ as a threatening substance and tries to rid the body of it.
relapse: The return of symptoms and disease after a person seems to have recovered.
relaxation response: The physical effects of meditation and certain other techniques that are opposite to those of the stress response. Effects include marked drops in oxygen consumption, carbon dioxide expiration, heartbeat, and respiration, as well as stabilization or lowering of blood pressure.
REM: Abbreviation for rapid eye movement, which occurs during a period of sleep characterized by intense brain activity, often associated with dreams.
REM behavior disorder: A sleep disorder marked by movement during REM sleep, when muscles are normally paralyzed.
REM rebound: An increase in REM sleep, often with nightmares, that occurs after deprivation of REM sleep or the withdrawal of REM-suppressing medications.
remission: A lessening in the severity of a disease and its symptoms. In cancer, a reduction in the size of a tumor and its symptoms.
remodeling: Altering a body part. Bone is constantly being remodeled in response to exercise or inactivity. Heart tissue is remodeled in response to a heart attack or high blood pressure.
renal: Pertaining to the kidneys.
renal artery stenosis: Narrowing of an artery that supplies blood to the kidney.
renin: An enzyme released by the kidney that stimulates production of angiotensin and aldosterone, two substances in the body that affect blood pressure.
reperfusion: Re-establishing blood flow, such as when a blockage in a coronary artery that is causing a heart attack is cleared.
reperfusion therapy: Techniques used to restart circulation to part of the heart or brain that has been cut off from blood flow during a heart attack or stroke. Reperfusion may entail clot-dissolving drugs, balloon angioplasty, or surgery.
repetitions: Number of times an exercise calls for a muscle to be worked and released (usually eight to 12). Often referred to as reps.
resection: The surgical removal of a lesion or part or all of an organ or other body structure.
resectoscope: An instrument that permits a surgeon to view the inside of a body cavity in order to remove a part of an organ or structure.
reservoir: The habitat in which an infectious agent normally lives, grows, and multiplies. Reservoirs include human, animal, and environmental reservoirs.
resilience: The ability to adapt to change and recover quickly from setbacks such as illness, injury, or misfortune.
resistance: The ability of a pathogen to withstand drugs previously effective against them. Usually the result of genetic mutation.
resistant hypertension: High blood pressure that does not respond to drug therapy and lifestyle changes.
resorption: The removal of bone tissue, both mineral and protein, by osteoclasts.
respiration: The process by which gases enter the body, including external respiration (breathing), and internal respiration, in which oxygen taken in by the lungs is carried by the blood to tissues and carbon dioxide is removed.
restenosis: Renarrowing of a blood vessel that has been widened with angioplasty.
resting energy expenditure: The rate at which the body burns calories while at rest. Resting energy expenditure accounts for 60%–75% of the daily calories burned.
restless legs syndrome: Achy or unpleasant feelings in the legs associated with a need to move. Most prominent at night, making it hard to fall asleep or stay asleep.
resuscitation: The process of reviving a person who is not breathing or whose heart is not beating using techniques such as artificial respiration and heart massage.
retina: The innermost layer of the eye, which converts light energy to electrical energy and sends visual images to the brain via the optic nerve.
retinal detachment: A condition in which the retina separates from the choroid (the back of the eye) and leads to a loss of vision.
retinoid: A synthetic, vitamin A-like compound.
retrieval: The act of recalling previously learned information, involving the reactivation of particular nerve-cell pathways in the brain related to that piece of information.
retrograde ejaculation: An adverse effect of both prostate surgery and some medications that causes semen to flow back into the bladder rather than out through the penis.
retrospective study: A research method that looks for possible causes for a current disease by examining a study population's past habits.
revascularization: Restoration of blood flow to areas of heart muscle affected by coronary artery disease by means of coronary artery bypass surgery or angioplasty.
reward insufficiency theory: The theory that some people turn to addiction to compensate for an inability to sufficiently experience pleasure.
reward pathway: An interrelated set of brain regions that are all involved in recognizing, experiencing, and remembering pleasurable or rewarding events.
rheumatic disease: Any one of over 100 disorders that cause inflammation in connective tissues.
rheumatism: Pain and stiffness of soft tissues in and around joints.
rheumatoid arthritis: An inflammatory autoimmune disease that typically attacks the connective tissue of the joints, causing them to become painful, inflamed, and sometimes deformed.
rheumatoid factor: An antibody found in about 85% of people with rheumatoid arthritis; also appears in other diseases and sometimes in healthy people.
rheumatologist: A medical doctor trained to diagnose and treat disorders involving inflammation of the joints and other parts of the musculoskeletal system.
rheumatology: The branch of medicine devoted to the study and treatment of diseases marked by inflammation, degeneration, or metabolic problems of the connective tissues (particularly the joints and related structures).
rhinoplasty: Reshaping the cartilage and bone of the nose to achieve the desired profile. Commonly known as a nose job.
rhytidectomy: A surgical procedure that involves removing excess skin and tightening the underlying muscle to correct sagging around the jaws, jowls, and neck. Does not include work on the eyes or forehead. Commonly known as a face lift.
right atrium: The right upper chamber of the heart; it receives partially deoxygenated blood as it returns from the body's tissues and moves it into the right ventricle for distribution to the lungs.
right coronary artery: One of the principal coronary arteries that supplies blood to the heart; this vessel supplies the right and lower part of the heart.
right ventricle: The right lower chamber of the heart; it receives blood from the right atrium for distribution to the lungs.
ringworm: An itchy condition of the scalp caused by a fungal infection. Also known as tinea capitis.
Rinne test: A simple hearing test that uses a tuning fork to determine what type of hearing loss a person has.
risk factor: Any factor that can cause a person to be more likely to develop a disease. For example, smoking is a risk factor for lung cancer.
risky drinking: Drinking that increases the chances of adverse consequences; drinking more than guidelines on moderate drinking suggest.
RLS: Abbreviation for restless legs syndrome, an achy or unpleasant feelings in the legs associated with a need to move. Most prominent at night, making it hard to fall asleep or stay asleep.
rods: Light-sensitive cells in the retina that respond best in darkness and dim light.
root: The portion of the tooth below the gum line.
root canal: A channel in the root of the tooth that contains the pulp.
root canal therapy: A procedure in which diseased pulp tissue is removed from the pulp chamber and root canal and the area is sealed off.
rosacea: A skin condition that enlarges blood vessels in the face, causing redness of the nose and other parts of the face.
rotator cuff: A group of tendons and muscles used to raise the arm from the side and rotating the shoulder.
roughage: Indigestible dietary fiber found in grains, fruits, vegetables, and other foods. Roughage is thought to help prevent conditions such as constipation.
rupture: A tear or break in an organ or tissue. Tissue that protrudes through the rupture is known as a hernia.
ruptured disk: When part of a spinal disk bulges out of a tear or weak spot in the disk's tough outer shell. Also known as prolapsed disk or herniated disk.
sacroiliitis: Inflammation of the sacroiliac joints, which connect the lower spine to the pelvis.
sacrum: The larger triangular bone at the base of the spine.
SAD: Abbreviation for seasonal affective disorder, sadness and depression brought on by a lack of exposure to sunlight. SAD usually appears in the fall or winter and subsides in the spring.
saline: A watery solution that contains a small amount of salt and is often used to administer drugs or as a substitute for plasma.
salivary gland: One of three pairs of glands that pour lubricating fluids and digestive enzymes into the mouth.
saphenous vein: A superficial blood vessel that extends from the thigh to the calf; it can be removed and used as a coronary bypass graft.
sarcolemma: A membrane that covers the muscle fiber and ties the end of it to a tendon.
sarcoma: A cancer that arises in the soft tissues of the body that connect, support, and separate other tissues or organs. Sarcomas can occur almost anywhere in the body.
satisficer: A person who can make a choice and be satisfied with it when presented with an option that meets his or her standards, without needing to examine all options or find the absolute best.
saturated fat: A type of fat found in animal foods such as meat, poultry skin, butter, and whole-milk dairy products, as well in as palm and coconut oils. A diet high in saturated fat tends to raise blood levels of unhealthy low-density lipoprotein (LDL) cholesterol.
sausage digit: A toe or finger swollen and red along its entire length.
scapulothoracic joint: A shoulder joint that connects the scapula to the ribs at the back of the chest.
Schlemm's canal: A circular drainage system in the eye located where the clear cornea, white sclera, and colored iris meet to form an angle.
sciatica: Pain along the course of the sciatic nerve (which runs from the buttock, down the back and side of the leg, and into the foot and toes), often because of a herniated disk.
scintigraphy: A diagnostic technique based on the detection of energy emitted by radioactive substances injected into the body; also called radionuclide scanning.
scintillations: The perception of flashing lights or lines that sometimes occurs during the aura of a migraine headache.
sclera: The white of the eye; a tough, protective coating of collagen and elastic tissue that, with the cornea, makes up the outer layer of the eyeball.
scleral buckling: A surgical technique that indents the sclera and choroid to reattach the retina.
scleroderma: An autoimmune disease in which the skin thickens and hardens; sometimes other parts of the body are affected, and joint pain may result.
scoliosis: An abnormal lateral, or sideways, curvature of the spine.
scotoma: A blank spot in the visual field that is sometimes evident during the aura of a migraine headache.
scurvy: A disease caused by vitamin C deficiency, characterized by bruising, poor wound healing, bleeding of the gums, and loosened teeth.
seasonal affective disorder: Sadness and depression brought on by a lack of exposure to sunlight. Seasonal affective disorder usually appears in the fall or winter and subsides in the spring. sometimes referred to as SAD.
sebaceous gland: A gland that opens into a terminal hair follicle; it secretes sebum, the natural oily conditioner of hair.
seborrheic dermatitis: A mild and common condition that is characterized by an itchy, flaky scalp and that may extend to the ears, face, and chest. Also known as dandruff.
secondary hypertension: High blood pressure that has an identifiable, often correctable, cause such as kidney disease, hyperthyroidism, sleep apnea and other conditions.
secondary osteoporosis: Bone loss associated with an identifiable medical condition, treatment with certain drugs, or immobility.
secretion: The release of chemical substances produced by the body; or the substance that is produced.
sed rate: Shorthand for erythrocyte sedimentation rate—a test involving red blood cells used to check for different infections, inflammations, and cancers.
sedative: A drug or a procedure that has a calming effect and relieves anxiety and tension.
seizure: A sudden, involuntary contraction of muscles that results in rhythmic contortions of the body, often accompanied by a loss of consciousness. Also called a convulsion.
selective estrogen receptor modulators: Chemically synthesized drugs that mimic estrogen in some tissues but act to block estrogen's effects in others.
selective serotonin reuptake inhibitors: Antidepressants that block the reuptake of serotonin into the neurons that released it, leaving more serotonin available to nerve cell receptors. Commonly used to treat depression and other mood disorders.
self-help group: A group of people who meet to discuss and offer assistance to one another with the goal of providing social support for changing troubling behavior patterns.
seminal vesicles: Structures surrounding the prostate gland involved in storing secretions made by the gland.
senescence: Gradual loss of body functions caused by the biological aging process, which increases risk of disease, disability, and death.
senile dementia: Diagnosis once given to people over 65 with dementia.
sensate focus techniques: A set of structured exercises that sex therapists use to help couples focus on the sensual aspects of physical contact without pressure to achieve orgasm.
sensorineural hearing loss: Permanent hearing loss caused by damage to the cochlea, hair cells, or auditory nerve.
sepsis: The destruction or infection of tissues by disease-causing organisms, usually accompanied by a fever.
septicemia: A condition in which disease-causing organisms have spread to the bloodstream from an infection elsewhere in the body. Also known as blood poisoning.
septum: A wall or other structure that divides one cavity from another. For example, in the heart the muscular septum separates the right side of the heart from the left side.
SERMs: Abbreviation for selective estrogen receptor modulators, chemically synthesized drugs that mimic estrogen in some tissues but act to block estrogen's effects in others.
seroma: A pocket of lymphatic fluid that builds up at an incision after surgery.
serotonin: A neurotransmitter that helps regulate sleep and appetite, mediate moods, and inhibit pain.
serotonin-norepinephrine reuptake inhibitors: Antidepressants that slow the reuptake of both serotonin and norepinephrine into the neurons that released these substances, leaving more serotonin and norepinephrine available to nerve cell receptors. Commonly used to treat depression and other mood disorders.
sesamoiditis: A painful inflammation in and around two small bones known as sesamoids, located beneath the base of the big toe, at the ball of the foot.
set: A specific number of repetitions of an exercise done as a group.
sexual dysfunction: A problem with any area of a person's sexual response that causes distress.
shock: A serious medical condition in which there too little blood flows to the outer portions of the body, resulting in cold, sweaty skin; a weak pulse; irregular breathing; and dilated pupils. Shock can be caused by a loss of blood, severe heart problems, severe infections, allergic reactions, or drug overdoses.
short-term memory: Information the brain stores temporarily, from milliseconds to minutes.
shunt: A device inserted into the body to redirect the flow of blood or other fluid from one area to another.
side effect: An unwanted, and sometimes dangerous, reaction caused by medication or other treatment.
sigmoid colon: Section of the colon leading to the rectum that makes an S-shaped curve.
sigmoidoscopy: Internal examination of the rectum and sigmoid colon using a flexible viewing tube inserted through the anus.
signature strengths: Character strengths such as curiosity, integrity, and modesty that people identify with, appreciate having, and enjoy using.
sildenafil citrate: The active ingredient in Viagra. It blocks the breakdown of cyclic guanosine monophosphate, a chemical necessary for an erection.
silent heart attack: Heart attack that occurs without pain or symptoms; occurs most commonly in the elderly or in people with diabetes.
silent ischemia: Shortage of oxygen delivery to the heart muscle that causes no symptoms.
single-photon absorptiometry: A test using gamma rays to measure bone density, usually in the forearm.
sinoatrial node: The natural pacemaker of the heart. Located in the right atrium, the sinoatrial node, sometimes called the sinus node, initiates the heart's electrical activity.
sinus node: A specialized group of heart cells in the right atrium that generate the electrical impulses that cause the heart muscle to contract. Also called the heart's natural pacemaker.
sinus rhythm: The heart's normal rate and rhythm.
skeletal muscles: Muscles attached to bones throughout the body that allow voluntary movement to occur.
skin resurfacing: Any of several approaches to improve skin texture, tone, wrinkle appearance, and discolorations by promoting new collagen and epidermal growth. Chemical peels, dermabrasion, microdermabrasion, and laser procedures are skin-resurfacing techniques.
sleep apnea: Temporary pause in breathing during sleep, lasting at least 10 seconds and associated with a fall in blood oxygen or arousal from sleep. Obstructive sleep apnea is caused by an obstruction in the airway blocking air flow; central sleep apnea occurs when the brain temporarily stops sending signals to the muscles that control breathing.
sleep architecture: The pattern made when sleep stages are charted on a hypnogram.
sleep paralysis: A feeling of paralysis that may occur during the transition between wakefulness and sleep if the REM sleep stage begins before a person is fully asleep; classically associated with narcolepsy.
sleep spindles: On an electroencephalogram (EEG), brief rhythmic bursts of activity that appear during stage 2 sleep.
sling: A slender piece of material surgically inserted under the urethra or bladder neck to provide support and improve continence.
slipped disk: See herniated disk.
slipped vertebra: Forward displacement of a vertebra in relation to the vertebra immediately below; also called spondylolisthesis.
slit lamp: An instrument that magnifies internal structures of the eye with the aid of a thin beam of light. Also called a biomicroscope.
slow-twitch fiber: One of two main types of skeletal muscle fibers. Slow-twitch fibers are recruited most heavily for endurance (aerobic) exercises. See also fast-twitch fiber.
slow-wave sleep: Sleep stages 3 and 4; during slow-wave sleep the brain becomes less responsive to external stimuli.
small intestine: A section of the digestive system that includes the duodenum, jejunum, and ileum and plays the major role in absorbing nutrients for the body.
SMART: An acronym for an approach to setting goals for behavioral change: set a very Specific goal; find a way to Measure progress; make sure it's Achievable; make sure it's Realistic; and set Time commitments.
Snellen chart: The conventional eye chart used to test vision with lines of block letters in progressively smaller sizes.
somatization: Bodily symptoms that have no clear physical cause or are out of proportion to a given ailment, and may stem from psychological causes.
somniloquy: Talking in one's sleep.
sorbitol: A crystalline sugar alcohol used as a sweetening agent.
spacer: A hollow chamber into which inhaled medicines can be squirted before inhalation. Spacers are used with metered-dose inhalers to help deliver medicine effectively to the bronchial tubes and to reduce the amount of medicine left behind on the tongue and throat.
spasm: An involuntary muscle contraction.
sphincter: A ring of muscle that surrounds an opening and can be contracted to close the opening. For example, the muscles found at the anus and the opening of the bladder are sphincters.
sphygmomanometer: A device for measuring blood pressure.
spina bifida: A congenital defect in which part of the spinal column fails to develop completely, leaving part of the spinal cord exposed.
spinal fusion: A procedure to attach two or more vertebrae with a bone graft in order to eliminate motion and relieve pain.
spinal stenosis: A narrowing of the spinal canal, which can result in compression of nerve roots.
spinal tap: Use of a hollow needle to withdraw fluid from the lower part of the spinal canal for testing. Also called a lumbar puncture.
spinous process: The lever-like backward projection extending off each vertebra, to which muscles and ligaments are attached.
spirometer: A device that measures airway obstruction, used to diagnose asthma and determine the severity of the condition.
spirometry: A simple, painless breathing test performed in a physician's office or pulmonary function laboratory that measures how fast air can be forced from the lungs and the total amount of air that can be emptied from the lungs.
splenic flexure syndrome: A painful spasm in the left upper abdomen below the rib cage, produced by areas of trapped gas in the colon.
spondylolisthesis: Forward displacement of a vertebra in relation to the vertebra immediately below.
spondylosis: A general term for degeneration of the spine that causes narrowing of the spinal canal and the small openings (intervertebral foramina) through which spinal nerves exit the canal.
spongy bone: Porous bone, also called trabecular bone, often found at the center of long bones.
sprain: A stretched or torn ligament.
sputum: A mixture of saliva and mucus that is coughed up from the respiratory tract. Sputum may be examined in a laboratory for signs of disease.
squamous cell: Flat, scaly epithelial cell.
SSRIs: Abbreviation for selective serotonin reuptake inhibitors, antidepressants that block the reuptake of serotonin into the neurons that released it, leaving more serotonin available to nerve cell receptors. Commonly used to treat depression and other mood disorders.
stable angina: Angina pectoris (chest pain with exertion or stress) that is well-controlled with medicines and lifestyle changes.
stable coronary artery disease: Narrowings in the heart arteries that cause angina pectoris in a predictable and stable pattern over time (for example, after walking a certain distance).
stages of change: A model for how people make changes in their lives. According to this model, changes in behavior are made gradually and in relatively distinct stages.
staging: The process of determining how far cancer has progressed. Staging is often used to determine the best course of treatment.
standardized extract: An herbal product in which what is believed to be the active ingredient meets an established standard of strength.
statins: Cholesterol-lowering medications that interfere with the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase; also known as HMG-CoA reductase inhibitors. Statins work by changing the way the liver processes lipids.
stenosis: An abnormal narrowing of a passageway, such as a blood vessel, or other type of opening in the body.
stent: A wire mesh device inserted into an artery to prop it open once a blockage has been cleared by angioplasty.
sterilization: 1) A surgical procedure or other method that results in a person being unable to reproduce. 2) The process by which materials are thoroughly cleaned of all organisms that could cause disease or infection.
steroids: Another term for corticosteroids—steroid medications made to mimic hormones produced naturally by the adrenal glands. They are used to treat a wide range of health problems.
stimulant: A substance that speeds up chemical reactions inside cells and provides a boost of energy. Examples include caffeine and amphetamine.
stomach: The sac-like organ of the digestive system between the esophagus and the duodenum which breaks down food and moves it along to the small intestine to be digested.
strain: A stretched or torn muscle or tendon, usually caused by accident, misuse, or overuse.
stratum corneum: The most superficial layer of the epidermis.
strength: The ability of muscles to exert force.
strength training: Popular term for exercises that harness resistance supplied by body weight, free weights such as dumbbells or weighted cuffs, resistance bands, or specialized machines; also known as resistance training or weight training.
streptokinase: A thrombolytic (clot-dissolving) agent designed to dissolve the blood clots that block an artery during a heart attack or stroke.
stress: An innate survival response in which certain hormones are released, increasing blood flow to the brain or heart. The stress response leads to an energy surge, enabling a person to flee dangerous situations. Ongoing stress, however, can sap energy and damage health.
stress fracture: A hairline crack in a bone that usually occurs from overuse; left untreated, this may lead to displacement of the bones.
stress response: Physiological changes, such as quickened breathing and heartbeat and increased blood pressure, brought on by stress hormones released in response to a real or perceived threat to safety. Also called the fight-or-flight response.
stress test: A diagnostic test in which cardiovascular measurements such as heart rate, blood pressure, and electrical activity are recorded while the heart is being stressed (usually by having the person exercise on a treadmill or bicycle).
stressors: Stressful events or circumstances that may be real or perceived threats to equilibrium and well-being.
stria: A line, streak, or band, such as the stretch marks that occur in pregnancy.
stricture: The abnormal narrowing of a hollow passage in the body, such as the esophagus or the urethra.
stroke: Blockage or rupture of a blood vessel supplying the brain; often leads to impaired brain function or death.
stupor: A state of lethargy and unresponsiveness.
subacute: A disease or condition that progresses slower than an acute condition but faster than a chronic condition.
subacute thyroiditis: A painful version of thyroid inflammation caused by viral infection. Symptoms are flu-like and include fever, muscle aches and pains, and a painful, swollen thyroid gland. Also known as de Quervain's thyroiditis.
subarachnoid hemorrhage: A hemorrhagic stroke that occurs when a blood vessel on the surface of the brain bursts and bleeds into the space between the brain and the skull; usually caused by an aneurysm or other blood vessel malformation.
subarachnoid space: Space inside the brain where cerebrospinal fluid circulates.
subcutaneous: Beneath the skin.
subcutaneous tissue: Deepest layer of skin, which consists of connective tissue and fat.
subdural hematoma: A blood clot in the brain between the cerebral cortex and the dura.
subendocardial myocytes: Heart-muscle cells on the inside of the heart chambers; these cells are highly susceptible to damage from blockages of the major coronary arteries.
substance abuse: Continued substance use despite substance-related social or interpersonal problems.
substance dependence: A condition characterized by excessive and often compulsive substance use, impaired control over substance use, continued use of substances despite adverse consequences, and withdrawal symptoms that emerge when the substance use is discontinued.
subunit vaccines: Vaccines using only part of a microbe—the antigens—to elicit an immune response; these vaccines tend to cause fewer adverse reactions than vaccines which contain the whole microbe.
sulcus: The V-shaped hollow at the margin of the tooth and gum.
sulfonylureas: A class of medications that works by stimulating the pancreas to produce more insulin.
sundowning: Confusion or disorientation beginning at the end of the day and continuing into the night; often occurs in people with Alzheimer's disease or vascular dementia.
superior vena cava: The major vein that carries deoxygenated blood from the upper body to the heart.
superset: Two or more exercises combined for a more vigorous workout. During a superset, all the reps of exercise A are performed and then all the reps of exercise B before resting.
suppository: A solid form of medication that is inserted in the rectum or vagina and absorbed into the bloodstream.
suprachiasmatic nucleus: A small group of nerve cells located in the hypothalamus that controls the sleep/wake cycle.
supraventricular tachycardia: An abnormally fast heartbeat originating in heart tissue above the ventricles.
suture: The process of sewing tissues together after surgery; or the stitch itself.
sympathetic nervous system: An offshoot of the autonomic nervous system; it sends signals to prepare the body for action when stress hormones are released in response to perceived or real dangers.
symptom-limited exercise stress test: Exercise test, usually using a treadmill or bicycle, that increases in difficulty at set stages and is stopped when the person develops chest pain, breathlessness, or extreme fatigue.
synapse: The junction between two neurons, across which chemical neurotransmitters carry messages.
syncope: Fainting or loss of consciousness caused by a temporary shortage of oxygen in the brain.
synovectomy: Surgical removal of the synovial membrane that lines the joints.
synovial fluid: A thick liquid that lubricates the joints and tendons.
synovial joint: The most mobile type of joint; found in the shoulders, wrists, fingers, hips, etc.
synovitis: Inflammation of the synovium.
synovium: A thin membrane that lines joint capsules and produces synovial fluid.
systemic: Pertaining to something that affects the whole body rather than separate organs or parts.
systemic lupus erythematosus: A connective tissue disease that can affect internal organs, nervous system, skin, and joints.
systole: The brief period during which the heart contracts during a normal heartbeat, pumping blood into the aorta and the pulmonary artery.
systolic blood pressure: The first or top number in a blood pressure reading; a measure of the pressure blood exerts against arterial walls when the heart contracts.
systolic heart failure: The inability of the heart to pump blood efficiently due to weakening and enlargement of the ventricles. Systolic heart failure is usually caused by coronary artery disease, high blood pressure, and valvular heart disease.
T cell: Abbreviation for T lymphocyte, a type of white blood cell that is produced in the bone marrow and is part of the body's immune system.
T lymphocyte: A type of white blood cell that is produced in the bone marrow and is part of the body's immune system. Also called a T cell.
tachycardia: An abnormally fast heartbeat, usually above 100 beats per minute.
tamoxifen: A drug used by women to prevent breast cancer or its recurrence.
tamsulosin: A drug used to treat symptoms of an enlarged prostate gland. It relieves constriction of the urethra and improves urine flow by relaxing the smooth muscle tissues in the capsule that surrounds the prostate. Unlike other drugs in this class, tamsulosin does not decrease blood pressure.
tangles: Also called neurofibrillary tangles—twisted strands of proteins that are found inside the dead or dying nerve cells of people with Alzheimer's disease.
tardive dyskinesia: Involuntary writhing movements of the arms, legs, and tongue caused by high doses of antipsychotic drugs over long periods of time.
tarsal coalition: An inherited condition in which two bones of the foot are fused together; can result in rigid flat feet.
tartar: A hardened layer of plaque that builds up on teeth. Also called calculus.
TDD: Abbreviation for telecommunications device for the deaf—machinery that allows a person who is deaf or hard of hearing to send and receive typed messages over the telephone.
telecommunications devices for the deaf: Machinery that allows a person who is deaf or hard of hearing to send and receive typed messages over the telephone.
tempo: When applied to exercise, the count for key movements in an exercise.
temporal arteritis: Also called cranial arteritis and giant cell arteritis—inflammation and damage to blood vessels supplying blood to the head and neck.
temporal lobe: One of the four major subdivisions of the two hemispheres of the brain's cerebral cortex. The temporal lobe plays a role in hearing, long-term memory, and behavior.
tendinitis: Inflammation of a tendon, usually caused by injury; may cause pain and restrict movement of the muscle attached to the tendon.
tendon: A cord of collagen fibers that connect a muscle to a bone.
tendonitis: Alternative spelling of tendinitis—inflammation of a tendon, usually caused by injury; may cause pain and restrict movement of the muscle attached to the tendon.
tenosynovitis: Swelling and inflammation of the protective sheath covering the tendons, which decreases the sheath's production of synovial fluid.
TENS: Abbreviation for transcutaneous electrical nerve stimulation—the use of low-voltage electrical current (through electrodes placed on the skin) to provide pain-suppressing stimulation.
tension headache: A headache, usually mild or moderate in intensity, not accompanied by other symptoms; pain is usually felt throughout the head, across the forehead, or in the back of the head. Also known as a muscle-contraction headache.
terazosin: A drug used to treat symptoms of an enlarged prostate gland. It relieves constriction of the urethra and improves urine flow by relaxing the smooth muscle tissue in the capsule that surrounds the prostate.
testosterone: A male hormone that stimulates bone and muscle growth and sexual development in men; also produced in lesser amounts in women, promoting sex drive and muscle growth.
thalamus: A brain structure that relays sensory information to other parts of the brain; also plays a role in memory consolidation.
theta waves: A pattern of brain waves on an electroencephalogram (EEG) characteristic of light, stage 1 sleep.
thiazolidinediones: A class of oral medication that improves sensitivity to insulin.
thoracic: Pertaining to the chest.
thrombolysis: Breaking up a blood clot.
thrombolytic agents: Agents or medications that dissolve blood clots and restore blood flow through a blocked artery; used to treat myocardial infarction, ischemic stroke, and pulmonary embolism. Also called clot busters. Examples include tissue plasminogen activator (tPA) and streptokinase.
thrombosis: Formation of a blood clot (called a thrombus) in a blood vessel or chamber of the heart.
thrombus: A blood clot that forms inside a blood vessel or chamber of the heart.
thunderclap headache: A sudden, excruciating headache that may be the result of bleeding in the head.
thymus: A specialized organ of the immune system located in the upper-middle chest where T cells mature.
thyroid gland: A two-lobed gland located in the front of the neck below the larynx (voice box). It secretes hormones that help regulate the body's metabolism and calcium balance.
thyroid hormone: Two iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3). They help regulate the body's metabolism and calcium balance.
thyroidectomy: A surgical procedure to remove all or part of the thyroid.
thyroiditis: Inflammation of the thyroid gland. Types of thyroiditis include Hashimoto's thyroiditis, subacute thyroiditis, and postpartum or silent thyroiditis.
thyroid-stimulating hormone: A hormone secreted into the bloodstream by the pituitary gland that stimulates the thyroid gland. Doctors measure levels of TSH to determine whether a person's thyroid hormone levels are normal.
thyrotoxicosis: The presence of too much thyroid hormone in the body. This may be caused by an overproductive thyroid, inflammation of the thyroid, or taking too much thyroid hormone.
thyroxine: One of two types of major thyroid hormone manufactured by the thyroid gland. It contains four iodine atoms. Also known as T4.
TIA: Abbreviation for transient ischemic attack, a brain attack that resolves on its own within 24 hours. Sometimes called a mini-stroke, a TIA is often an early warning sign of an impending stroke.
tibia: The large bone of the calf, or shinbone.
tic douloureux: Pain from a disorder of the trigeminal nerve, the chief sensory nerve of the face. Also called trigeminal neuralgia.
ticlopidine: An antiplatelet drug that prevents the formation of blood clots.
tincture: An herbal product made by soaking an herb or other plant material in a mixture of water and alcohol to extract certain ingredients believed to be medicinal or beneficial.
tinea capitis: An itchy condition of the scalp caused by a fungal infection. Also known as ringworm.
tinea pedis: Athlete's foot.
tinnitus: A ringing in the ears or some other sound that has no external cause.
tissue: A group of cells that are specialized to do a certain job and are joined together to form a body structure, such as muscle or kidney.
tissue plasminogen activator: A clot-dissolving enzyme produced naturally in the blood vessels and artificially produced as a medication. Tissue plasminogen activator (commonly known as tPA) is used to break down blood clots in the treatment of heart attack, ischemic stroke, and pulmonary embolism. tPA must be used within a few hours after symptoms begin.
tolerable upper intake level: The highest amount of a nutrient deemed likely to have no harmful health effects for almost all healthy people when taken consistently.
tolerance: The process through which the body becomes less responsive to a psychoactive substance or rewarding behavior. Over time, people who develop tolerance need larger doses to get the same effect they first got with smaller doses.
toll-like receptors: One class of pattern-recognition receptors, found on the surfaces of the cells of the innate immune system.
tonic: An agent believed to invigorate a specific body organ.
tonometry: A glaucoma screening test that measures pressure inside the eye.
tooth decay: Infectious disease that attacks the teeth. Also called dental caries.
topical: Pertaining to an external surface of the body, such as the skin, mouth, vagina, or anus; often used to describe the administration of medicine that is applied directly to such a surface.
toxic: Pertaining to something that is poisonous.
toxic nodular goiter: An enlarged thyroid gland with nodules that produce excess thyroid hormone. This type of goiter is to blame for hyperthyroidism in many people over 60.
toxin: A poison, usually one produced by a living organism.
toxoid vaccines: Vaccines that protect against harmful bacterial toxins. These vaccines contain toxins that have been detoxified and rendered inactive.
tPA: Abbreviation for tissue plasminogen activator, a clot-dissolving enzyme produced naturally in the blood vessels and artificially produced as a medication. tPA is used to break down blood clots in the treatment of heart attack, ischemic stroke, and pulmonary embolism. tPA must be used within a few hours after symptoms begin.
trabecular bone: Bone tissue arranged in a meshwork of thin plates or beams that is commonly found at the center of long bones and that composes a large part of the hip and vertebrae. Also called cancellous bone or spongy bone.
trabecular meshwork: A system of fine, mesh-like tissue in the anterior chamber of the eye through which aqueous humor drains; located in the angle where the clear cornea, white sclera, and colored iris join.
trabeculectomy: A standard surgical procedure for glaucoma that creates a new channel for fluid drainage from the anterior chamber to the sub-conjunctival space.
trabeculoplasty: A laser procedure that burns small holes on the eye's trabecular meshwork to ease the flow of aqueous humor from the eye.
trace mineral: A mineral that is required only in tiny amounts in the diet to maintain health; the principal trace minerals are chromium, copper, selenium, sulfur, and zinc.
tracheostomy: A hole created through the front of the neck and into the windpipe (trachea). It provides an air passage when the usual route for breathing is obstructed, such as after a traumatic injury to the face or neck, or when long-term use of a breathing machine (ventilator) is needed.
tracheotomy: The procedure used to create a tracheostomy.
traction: The process of putting a bone or other body part under a pulling tension by applying weights and pulleys to help healing.
trans fatty acid: A type of fat made during hydrogenation of liquid vegetable oil. Trans fats are found in many solid margarines, commercially prepared baked goods, and fried foods in many restaurants. Trans fats increase harmful low-density lipoprotein, decrease protective high-density lipoprotein, and promote blood clotting and inflammation. Also known as trans fat.
transcranial Doppler scanning: An ultrasound technique that makes images of the major arteries at the base of the brain.
transcutaneous electrical nerve stimulation: The use of low-voltage electrical current (through electrodes placed on the skin) to provide pain-suppressing stimulation.
transdermal: Through the skin.
transferrin saturation: A measure of iron circulating in the blood.
transfusion: The process of taking blood from a healthy person and infusing it into a person whose own blood has been depleted during surgery or an accident, or is for some reason not functioning correctly. Transfusions of whole blood or of specific blood cells (such as red cells, white cells, or platelets) are possible.
transient ischemic attack: A brain attack that resolves on its own within 24 hours. Sometimes called a mini-stroke or TIA, a transient ischemic attack is often an early warning sign of an impending stroke.
transient pain: Minor, fleeting pain.
transmural infarction: Heart attack that destroys the entire thickness of a section of heart muscle.
transplantation: The process of removing an organ or other donated body part from one person and implanting it in another person.
transrectal ultrasonography: A procedure that uses sound waves to create an image of the prostate gland as a means of detecting cancer. Sound waves are directed to the prostate from a probe inserted in the rectum.
transurethral incision of the prostate: An operation used to treat benign prostatic hyperplasia (enlarged prostate gland) in which incisions are made in prostate tissue to relieve pressure on the urethra and ease urinary difficulties.
transurethral microwave thermotherapy: A heat therapy for benign prostatic hyperplasia (enlarged prostate gland) that uses microwaves to destroy prostate tissue that obstructs urine flow.
transurethral needle ablation: A procedure that uses radio waves to heat and destroy cells in the prostate gland that are obstructing the urethra.
transurethral resection of the prostate: An operation used to treat benign prostatic hyperplasia (enlarged prostate gland) in which excess prostate tissue is surgically removed.
transverse processes: The ringlike projection on each side of a vertebra to which muscles and ligaments are attached and, in the chest area, to which the ribs are connected.
traumatic grief: A prolonged, intense reaction to bereavement that affects one in 10 people who lose a loved one. Key signs are inability to accept the death; frequent nightmares and intrusive, upsetting memories; detachment from others; constant yearning for the deceased; and excessive loneliness. Also known as complicated grief or chronic grief.
tremor: A rhythmic, quivering movement of muscles that can be caused by diseases such as Parkinson disease, side effects of medication, or old age.
tricuspid valve: A three-flap valve that sits between the right atrium and the right ventricle.
tricyclic antidepressant: A class of medications that relieve depression by interfering with the reuptake of serotonin and norepinephrine by neurons in the brain and spinal cord. At low doses, they are effective as pain medicines.
trigeminal neuralgia: Pain from a disorder of the trigeminal nerve, the chief sensory nerve of the face. Also called tic douloureux.
trigger: Anything that can set off symptoms.
trigger point: A tender area that, when stimulated, also elicits pain elsewhere in the body.
triglyceride: The primary type of fat in the body and in the diet, formed from three fatty-acid molecules and one glycerol molecule. This fat can raise the risk for heart disease when elevated.
triiodothyronine: One of two types of major thyroid hormone manufactured by the thyroid gland. It contains three iodine atoms. Also known as T3.
triptans: A class of medications that work by constricting blood vessels in the head and perhaps by inhibiting inflammation.
trochlea: A groove in front of the femur where the patella moves as the knee bends and straightens.
troponins: Proteins found in heart muscle that leak into the circulation during a heart attack or other heart injury.
trust: A legal entity in which assets are gathered during a person's lifetime. That person may control distributions directly or through trustees elected to carry out wishes at a time or point specified. After death, remaining assets are distributed to beneficiaries.
trypsin: An enzyme secreted by the pancreas that helps digest proteins.
TSH: Abbreviation for thyroid-stimulating hormone, a hormone secreted into the bloodstream by the pituitary gland that stimulates the thyroid gland. Doctors measure levels of TSH to determine whether a person's thyroid hormone levels are normal.
tumor: Any type of swelling or enlargement of tissues; most often used to describe an abnormal growth of tissue, which can be cancerous or noncancerous.
tunica albuginea: The dense fibrous membrane surrounding each corpus cavernosum and the corpus spongiosum in the penis.
tympanic membrane: The eardrum.
tympanometry: A test of the eardrum's motion and pressure in the middle ear. Also known as impedance testing.
type 1 diabetes: A type of diabetes, a chronic condition that affects the way the body's tissues use sugar (glucose), their main source of fuel. Once called juvenile-onset diabetes and insulin-dependent diabetes. People with this form of diabetes don't make enough insulin, a hormone that controls the movement of glucose into cells. They must rely on insulin injections.
type 1 osteoporosis: Bone loss due to estrogen decline associated with menopause.
type 2 diabetes: A type of diabetes, a chronic condition that affects the way the body's tissues use sugar (glucose), their main source of fuel. Once called adult -onset diabetes and non-insulin-dependent diabetes. People with this form of the disease have tissues that either resist the effects of insulin (a hormone that control the movement of sugar into cells) or the body doesn't produce enough insulin. It is initially treated with diet, exercise, weight-loss if needed, and oral medications.
type 2 osteoporosis: Bone loss due to aging.
ulcer: A break in the skin or other surface that often occurs along with inflammation, infection, or cancerous growth.
ultrasound: A painless, noninvasive imaging method that uses high-frequency sound waves.
unopposed estrogen: Estrogen taken without an accompanying progestogen.
unresolved losses: Personal losses that are not acknowledged and mourned. Many mental health experts believe that reactions to these losses crop up later, often skewing a person's response to an entirely different loss.
unsaturated fat: Healthy dietary fats from plant sources such as vegetable oils, nuts, and whole grains, as well as from fatty fish. Includes monounsaturated fat and polyunsaturated fat.
unstable angina: Chest pain that occurs or worsens in frequency, severity, or duration when a person is at rest or engaging in mild activity.
upper airway resistance syndrome: Inhalation that requires undue extra exertion; this extra work may cause insomnia and daytime sleepiness.
upper esophageal sphincter: Muscular valve located at the upper portion of the esophagus that opens to allow food or liquid to enter the digestive system.
urea: A waste product of protein digestion and metabolism.
ureter: The tube that connects each kidney to the bladder.
urethra: The tube leading from the bladder through which urine is carried from the body.
urethral hypermobility: Movement of the urethra out of place when abdominal pressure increases, leading to stress incontinence.
urethritis: Inflammation of the urethra.
urgency: The sudden and uncontrollable need to urinate or defecate.
urinary frequency: Routinely needing to urinate more than eight times during the day or more than twice at night.
urinary incontinence: Inability to control urine flow, resulting in involuntary discharge or leakage.
urinary tract: Part of the body that produces and excretes urine. It consists of the kidneys, ureters, bladder, and urethra.
urologist: A specialist who deals with the urinary tract and male reproductive system.
urticaria: An itchy rash of usually short duration. Also known as hives.
uveitis: Inflammation of the pigmented part of the eye (the iris); may seriously affect vision.
uvula: A small, fleshy flap of tissue that hangs from the back of the throat over the root of the tongue.
uvulopalatopharyngoplasty: A surgical treatment for obstructive sleep apnea that involves removing the uvula, the tonsils, and a rim of loose tissue at the back of the soft palate.
vaccination: A method of protecting the body against disease by injecting parts or all of a microorganism that will cause the body to develop antibodies against the microorganism and later fight off disease.
vacuum erection devices: Various manual or battery-operated pumps that a man can use to draw blood into the penis to create an erection.
vaginismus: Spasms of the muscles around the vaginal opening that prevent penile penetration.
valves: Structures consisting of leaflets that divide the chambers of the heart and prevent the backflow of blood from one chamber to another during contraction of the heart.
variant angina pectoris: Also called Prinzmetal's angina, these are attacks of chest pain caused by spasms of one or more coronary arteries almost always while a person is at rest.
vascular: Having to do with blood vessels and circulation.
vascular dementia: Dementia caused by narrowing or blockage of blood vessels in the brain or by a stroke or series of tiny strokes. Also called multi-infarct dementia.
vascular surgery: An operation to improve blood flow either by repairing leaks in blood vessels or by rerouting arteries to bypass blockages.
vasculitis: Inflammation of blood vessels.
vasectomy: An operation that ties off or cuts the tubes through which sperm travel from the testicles to the urethra; used as a form of birth control.
vasoconstrictor: A substance or condition, such as drugs, cold, fear, and nicotine, that causes blood vessels to narrow and thus de-creases the flow of blood.
vasodilation: A widening of the blood vessels that results in increased blood flow.
vasodilator: A substance or condition that causes blood vessels to open wider and increase the flow of blood.
vasospasm: Uncontrollable contraction or spasm of a blood vessel.
vector: An animal or insect that transmits an infectious disease from a reservoir to a susceptible host.
vein: A vessel that carries blood back to the heart.
venous: Pertaining to a vein.
venous leak: Seepage of blood out of a vein.
ventilator: Machine that inflates the lungs with oxygen.
ventricle: One of the two lower chambers of the heart. The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body.
ventricular arrhythmia: Abnormal heart rhythm that starts in the lower chambers of the heart; this rhythm disturbance can occur as a complication of a heart attack and impairs the heart's pumping ability.
ventricular fibrillation: A deadly heart rhythm in which the ventricles contract independently of the atria and in a chaotic manner.
ventricular myocardium: Heart muscle that makes up the lower chambers of the heart.
ventricular rupture: Break in the heart muscle that allows blood to escape into the pericardial sac.
ventricular septal defect: One or more holes in the septum, the muscular wall separating the right and left sides of the heart.
ventricular tachycardia: A very fast heartbeat that starts in the ventricles. Ventricular tachycardia can be deadly if it renders the heart unable to pump enough blood to the body.
venules: Small veins.
vertebra: One of the cylindrical bones that form the spine (plural: vertebrae).
vertebral artery: One of two blood vessels that run up the back of the neck and join at the base of the skull to form the basilar artery. The vertebral arteries carry blood from the heart to the brain.
vertebroplasty: A minimally invasive procedure to stabilize compressed vertebrae and alleviate pain. A needle is inserted into the compressed portion of a vertebra and surgical cement is injected to support the vertebra and prevent further collapse.
vertigo: Dizziness; often a spinning sensation or a feeling that the ground is tilting.
very low-calorie diet: A weight-loss diet that allows 800 or fewer calories per day (usually followed under medical supervision).
very-low-density lipoprotein: A lipoprotein that transports triglyceride manufactured in the liver to fat tissue in the body. VLDL eventually becomes low-density lipoprotein (LDL) after the triglyceride has been removed.
vestibular system: The balance organs, located in the labyrinth in the inner ear.
viral: Pertaining to or caused by a virus.
virtues: Core characteristics that are universally valued by philosophers and religions across time and cultures, such as wisdom and courage.
virulent: A disease or condition that is highly infectious or dangerous or rapidly progressing.
viscera: The internal organs, especially those found in the abdomen.
visceral fat: Fat that lies beneath the abdominal wall, in the spaces surrounding the liver, intestines, and other organs. Sometimes called belly fat or abdominal adiposity.
visual acuity: The eye's ability to see sharply, usually measured in comparison to what a normal eye would see from 20 feet. Problems in visual acuity can usually be corrected with eyeglasses.
visual cortex: The part of the occipital lobe in the brain that processes visual stimuli.
visual field: The full scope of what the eye sees; includes central and peripheral vision.
visualized laser-assisted prostatectomy: A technique used to treat benign prostatic hyperplasia (enlarged prostate gland) that allows the surgeon to view the prostate directly while it is being shrunk by a laser beam.
vital signs: Measurements that indicate how well the body is functioning, including pulse rate, respiration (breathing rate), temperature, and blood pressure.
vitamin D: A hormone that plays a key role in ensuring the absorption of calcium from the intestines.
vitrectomy: A microsurgical procedure in which part of the vitreous humor of the eye is removed and then replaced with sterile saline or some other fluid.
vitreous humor: The clear, gel-like substance that fills the space behind the lens of the eye and supports the shape of the rear portion of the eye.
VLDL: Abbreviation for very-low-density lipoprotein, a lipoprotein that transports triglyceride manufactured in the liver to fat tissue in the body. VLDL eventually becomes low-density lipoprotein (LDL) after the triglyceride has been removed.
VO2 max: The body's maximum capacity for oxygen consumption during peak exertion. Also known as aerobic power, maximal oxygen consumption, or cardiorespiratory endurance capacity.
volatile oils: Unstable components of a preparation that evaporate easily.
VSD: Abbreviation for ventricular septal defect—one or more holes in the septum, the muscular wall separating the right and left sides of the heart.
vulnerary: An agent that is believed to aid in wound healing.
vulvar vestibulitis: Inflammation of the tissue around the opening of the vagina that makes sexual activity painful.
vulvodynia: Pain in the vulva that may or may not be brought on by touch or pressure.
wall stress: Force on the wall of the heart muscle caused by pressure inside the heart's pumping chamber; excessive wall stress can impair the heart's ability to pump and increase the heart's need for oxygen.
warfarin: An anticoagulant drug that prevents blood clotting; people taking it must have regular blood tests to determine that their blood does not clot too readily or too slowly.
wart: An abnormal fibrous growth caused by a viral infection.
water brash: Salty-tasting salivary secretions stimulated by gastroesophageal reflux.
Weber test: A hearing test that uses a tuning fork to diagnose one-sided hearing loss.
Wernicke-Korsakoff syndrome: An irreversible state of acute confusion and amnesia that develops in alcoholics as a result of malnutrition-related thiamine deficiency.
Wernicke's area: The brain region responsible for the comprehension of speech.
whiplash: The popular term for muscle and ligament damage resulting from rapid and extreme extension and flexion of the neck. The term is also used for the accident causing the injury, most often a rear-end motor vehicle accident.
white matter: The inner portion of the brain, composed primarily of axons, each surrounded by a myelin sheath that insulates the nerve fibers (and appears white). Messages are sent between different regions of the brain (gray matter) via these nerve fibers.
white-coat hypertension: Blood pressure that is elevated in a doctor's office but is normal at home.
will: A legal document that describes what should be done with a person's assets after his or her death.
withdrawal: A response to danger or stress characterized by apathy, lethargy, and depression; or the physical or psychological response to a sudden lack of an addictive substance such as alcohol or nicotine.
working memory: A type of short-term memory process that involves temporarily storing and manipulating information.
xanthelasma: A xanthoma on the eyelid.
xanthoma: A yellow, lipid-laden deposit in the skin or on a tendon.
YAG capsulotomy: A laser technique to correct blurred vision caused by cloudiness that may develop in the skin of the cataract left in the eye after cataract surgery; a laser is used to create a hole in the membrane to allow light to enter clearly focused onto the retina.
yohimbine: An extract of the bark of a West African tree sometimes used in treating erectile dysfunction. Yohimbine appears to increase blood flow to the penis and prevent blood from leaving it too quickly.
zonules: Thin, gelatinous ligaments that attach the lens to the ciliary body and support the lens centrally behind the pupil.
zoonotic disease: An infectious disease that is transmissible under normal conditions from animals to humans.