amyotrophic lateral sclerosis A progressive chronic disease of nerves from the spinal cord that are responsible for supplying electrical stimulation to the muscles. Abbreviated ALS. ALS is progressive and usually fatal in less than eight years, from illnesses that strike as the body becomes weaker. ALS occurs most often in adults over 50. The cause…
amyloidosis A group of diseases that result from the abnormal deposition of a protein, called amyloid, in various tissues of the body. Amyloid protein can be deposited in a localized area, and it may not be harmful or it may affect only a single tissue of the body. This form of amyloidosis is called localized…
amygdala 1 The amygdaloid nucleus in the brain. 2 The tonsils. These structures were so named because they appeared to be shaped like an almond.
AMS 1 Atypical measles syndrome. 2 Acute mountain sickness.
amputation Removal of part or all of a body part that is enclosed by skin. Amputation can occur at an accident site, the scene of an animal attack, or a battlefield. Amputation is also performed as a surgical procedure. It is typically performed to prevent the spread of gangrene as a complication of frostbite, injury,…
ampulla of Vater A small projection into the duodenum through which bile and pancreatic secretions flow to mix with food for digestion.
amplification An event that produces multiple copies of a gene or of any sequence of DNA. Gene amplification plays a role in cancer. Amplification can occur in vivo (in the living individual) or in vitro (in the laboratory).
amphetamine A drug that has a stimulant effect on the central nervous system that can be both physically and psychologically addictive when overused. Amphetamine has been much abused recreationally. The street term “speed” refers to stimulant drugs such as amphetamine.
amniotic fluid The fluid bathing a fetus within the uterus, which serves as a shock absorber.
amnion A thin membrane that surrounds the fetus during pregnancy. The amnion is the inner of the two fetal membranes (the chorion is the outer one), and it contains the amniotic fluid.
amniocentesis A before-birth diagnostic procedure during which a long needle is used to obtain amniotic fluid from within the uterus. This fluid can be used for genetic and other diagnostic tests. Informally known as amnio.
amnesia An impairment to or lack of memory. Antegrade amnesia refers to a lack of memory of events occurring after a traumatic event, whereas retrograde amnesia refers to lack of memory of events that occurred before the event.