Webster's New World Medical Dictionary

urethral sphincter
A muscular mechanism 
that controls the retention and release of urine from
the bladder. There are two urethral sphincters: the
internal and external urinary sphincters. Part of the
muscular bladder wall acts as the internal urethral
sphincter and prevents urine from leaving the blad-
der to enter the urethra. This sphincter cannot be
willfully controlled but is under involuntary control
by the brain. A layer of muscle called the urogenital
diaphragm supplies support for the contents of the
pelvis and acts as the external urethral sphincter. It
provides a second means of stopping the escape of
urine from the body. This sphincter is under volun-
tary control.
urethritis
Inflammation of the urethra, the tube
that leads from the bladder to the outside of the
body. Urethritis can have a number of causes,
including irritation and sexually transmitted dis-
eases such as chlamydia. Urethritis is closely asso-
ciated with bacterial infection of the bladder
(cystitis).
urethroscope
A device for examining the inside
of the urethra.
URI
Upper respiratory infection. Infection of the
air passages of the nose, the throat, and/or
bronchial tubes.
uric acid
A substance that is produced when pro-
teins are metabolized. In gout, elevated levels of uric
acid are commonly found in the blood (hyper-
uricemia). However, only a small portion of people
with hyperuricemia actually develop gout. See also
gout.
uricaciduria
The presence of excess uric acid in
the urine, which may be a sign of gout or kidney
stones.
urinalysis
A test that is done in order to analyze
urine. Because toxins and excess fluid are removed
from the body in urine, analysis of urine can pro-
vide important health clues. Urinalysis can be used
to detect certain diseases, such as diabetes, gout,
and other metabolic disorders, as well as kidney
disease. It can also be used to uncover evidence of
drug abuse. Accurate urinalysis may require a
“clean catch” of urine. Before a person gives a
urine sample, he or she should drink plenty of flu-
ids and wait until 1 or 2 seconds into the flow of
urine before catching the urine in the receptacle.
For some tests it is important to get the first urine of
the day, which contains the highest concentration of
toxins and other substances to be analyzed. For
other tests, a 24-hour collection of urine may be
needed.
urinary
Having to do with the function or
anatomy of the kidneys, ureters, bladder, or ure-
thra. For example, the urinary tract is the collection
of organs of the body that produce, store, and dis-
charge urine.