Medical Dictionary of Health Terms: A-C

Medical Dictionary of Health Terms: A-C

Browse dictionary by letter:
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z


5-alpha reductase: A chemical that changes the sex hormone testosterone into a substance called dihydrotestosterone. This hormone can cause the prostate gland to grow abnormally.

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.

Browse dictionary by letter:
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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.

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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.

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No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

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