Dictionary

A In genetics, adenine, a member of the adeninethymine (A-T) base pair in DNA.

a- Prefix indicating the absence or depletion of something: for example, aphagia (not eating) or aphonia (voiceless). The related prefix an- is usually used before a vowel, as in anemia (without blood) and anoxia (without oxygen).

AA 1 Alcoholics Anonymous. 2 Amino acid.

AAAS American Association for the Advancement of Science, a professional organization that publishes the weekly journal Science.

AAFP 1 American Association of Family Physicians, a professional organization for physicians who treat both children and adults. 2 American Academy of Family Physicians, a professional organization for physicians who treat both children and adults.

AAO 1 American Association of Ophthalmology, a professional organization. 2 American Association of Orthodontists, a professional organization. 3 American Academy of Otolaryngology, a professional organization.

AAOS American Academy of Orthopaedic Surgeons, a professional organization. See also orthopaedics.

AAP 1 American Academy of Pediatrics, a professional organization for physicians who treat infants, children, adolescents, and young adults. 2 American Academy of Pedodontics, a professional organization. 3 American Academy of Periodontology, a professional organization. 4 American Association of Pathologists, a professional organization.

ab- Prefix indicating from, away from, or off, as in abduction (movement of a limb away from the midline of the body) and abnormal (away from normal).

abdomen The part of the body that contains all the structures between the chest and the pelvis. The abdomen, or belly, is anatomically separated from the chest by the diaphragm, the powerful muscle that spans the body cavity, just below the lungs. See also abdominal cavity.

abdominal aorta The final section of the aorta, the largest artery in the body, which begins at the diaphragm as a continuation of the thoracic aorta and ends by splitting in two, to form the common iliac arteries. The abdominal aorta supplies oxygenated blood to all the abdominal and pelvic organs, as well as to…

abdominal aortic aneurysm See aneurysm, abdominal aortic.