Dictionary

Body systems

Anatomy and the conditions of each body system, from the heart and lungs to the skin.

allergic reactionA harmful response of the immune system to a substance that is harmless to most people.

allergyA reaction of the immune system to a substance that is harmless to most people.

alopeciaLoss of hair from the head or body.

alveolusOne of the tiny air sacs at the ends of the smallest airways in the lungs.

Alzheimer diseaseA brain disease that slowly destroys memory, thinking and the ability to do everyday tasks.

amenorrheaThe absence of menstrual periods.

American Heart AssociationA US nonprofit group that funds heart and stroke research and publishes guidelines, including for CPR.

amino acidOne of the small building blocks that join together in chains to make proteins.

amniotic fluidThe fluid inside the amniotic sac that surrounds and protects the baby during pregnancy.

amputationThe removal of all or part of a limb or other body part, by surgery or by injury.

amyotrophic lateral sclerosisA disease in which the nerve cells that control voluntary muscles slowly die.

anaphylaxisA sudden, severe allergic reaction that affects the whole body.

anastomosisA connection between two tube-shaped structures, such as two ends of bowel or two blood vessels, made by surgery or found naturally.

anatomyThe study of the structure of the body and its parts.

androgenA male sex hormone, such as testosterone, or a drug that acts like one.

anemiaA lower than normal number of red blood cells or amount of hemoglobin in the blood.

aneurysmA weak spot in the wall of an artery that bulges outward like a balloon.

anginaChest pain or pressure that happens when the heart muscle does not get enough blood and oxygen.

angioedemaSwelling in the deeper layers of the skin and the lining of the mouth, throat or gut.

angiogenesisThe growth of new blood vessels.

anorexiaA loss of appetite or of the wish to eat; also short for anorexia nervosa, an eating disorder.

anorexia nervosaAn eating disorder in which a person limits food intake out of an intense fear of gaining weight and a distorted view of their own body.

anteriorAt or toward the front of the body.

anthraxA serious infection caused by the spore-forming bacterium Bacillus anthracis.

antibodyA Y-shaped protein made by the immune system that sticks to one specific germ or foreign substance and marks it for destruction.

antidiuretic hormoneA hormone from the pituitary gland that tells the kidneys to hold on to water, making the urine more concentrated.

antigenA substance, often a protein on a germ or cell, that the immune system recognizes and responds to.

antioxidantA substance that protects cells from damage caused by unstable molecules called free radicals.

anuriaMaking little or no urine: less than about 50 to 100 mL in 24 hours in an adult.

anusThe opening at the lower end of the bowel where stool leaves the body.

anxietyA feeling of worry, fear or unease about something that may happen, often with physical signs such as a racing heart.

anxiety disorderA mental health condition in which anxiety is excessive, lasting and hard to control, and gets in the way of daily life.

aortaThe body's largest artery, which carries oxygen-rich blood from the heart's left ventricle to the rest of the body.

aortic valveThe heart valve between the left ventricle and the aorta, which opens to let blood out to the body.

aphagiaInability to swallow.

aphasiaLoss or impairment of the ability to understand or use language, from damage to the brain.

apicalRelating to the apex, the tip or top of a structure; most often used for the apical pulse, heard at the tip of the heart.

apical pulseThe heartbeat counted by listening with a stethoscope over the tip (apex) of the heart, on the left side of the chest.

aplastic anemiaA rare condition in which the bone marrow stops making enough red cells, white cells and platelets.

apneaA pause in breathing, or breathing that has stopped.

apoptosisProgrammed cell death: an orderly process by which the body removes cells it no longer needs.

appendicitisInflammation of the appendix, the small pouch that hangs from the start of the large intestine.

appendixA small, finger-shaped pouch attached to the first part of the large intestine, in the lower right abdomen.

apraxiaInability to carry out a learned, purposeful movement even though the person has the strength, feeling and wish to do it.

arrhythmiaA heart rhythm that is not normal: too fast, too slow or irregular.

arterial lineA thin catheter placed in an artery, often in the wrist, to measure blood pressure all the time and draw blood.

arterioleA very small artery that carries blood from an artery into the capillaries.

arteriosclerosisThickening and stiffening of the walls of the arteries, so they lose their ability to stretch.

arteriovenousRelating to both arteries and veins, or joining an artery to a vein.

arteriovenous fistulaA connection made by surgery between an artery and a vein, usually in the arm, to give access for hemodialysis.