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.