Webster's New World Medical Dictionary

anus
The opening of the rectum to the outside of
the body.
anus, imperforate
A birth defect in which the
rectum is a blind alley and there is no anus.
Imperforate anus occurs in about 1 in 5,000 births,
and it can be corrected by surgery.
anxiety
A feeling of apprehension and fear, char-
acterized by physical symptoms such as palpita-
tions, sweating, and feelings of stress.
anxiety disorder
A chronic condition character-
ized by an excessive and persistent sense of appre-
hension, with physical symptoms such as sweating,
palpitations, and feelings of stress. Treatments
include the comfort offered by understanding the
condition, avoiding or desensitizing exacerbating sit-
uations, and medications.
aorta
The largest artery in the body, the major
conduit from the heart to the body. The aorta arises
from the left ventricle of the heart, ascends a little,
arches, and then descends through the chest and
the abdomen, ending by dividing into two arteries,
the common iliac arteries, that supply blood to the
lower extremities. Anatomically, the aorta is tradi-
tionally divided into the ascending aorta, the aortic
arch, and the descending aorta. The descending
aorta is, in turn, subdivided into the thoracic aorta,
which goes from the heart to above the diaphragm,
and the abdominal aorta, which is below the
diaphragm. The aorta has branches to the head and
neck, the arms, the major organs in the chest and
abdomen, and the legs. It supplies them all with
oxygenated blood. See also 
abdominal aorta;
ascending aorta; descending aorta; thoracic
aorta.
aorta, coarctation of the
A constriction of the
aorta. At the point of coarctation, the sides of the
aorta appear to be pressed together. Blood pressure
is increased above the constriction, and the flow of
blood is impeded below the level of the constriction.
Symptoms may not be evident at birth but can
develop as soon as the first week after birth, with
congestive heart failure or high blood pressure that
call for early surgery. The outlook after surgery is
usually favorable. Some cases of coarctation of the
aorta have been treated with balloon angioplasty.