Webster's New World Medical Dictionary

part of the gastrointestinal tract (the esophagus,
stomach, and small intestine) that are taken after a
patient drinks a barium solution. See also 
barium
solution; barium swallow.
upper leg
See 
leg, upper.
urachus
A canal that connects the urinary blad-
der to the umbilicus (bellybutton) during fetal
development. The urachus is normally obliterated,
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so it is usually a solid cord. Failure for the urachus
to fill in leaves it open. The telltale sign of an open
urachus is leakage of urine through the umbilicus.
An open urachus is a malformation and needs to be
surgically corrected.
uracil
One of the nucleotide bases in RNA. Uracil
takes the place in RNA that thymine occupies in
DNA. Abbreviated U.
urate
A salt that is derived from uric acid. When
the body cannot metabolize uric acid properly,
urates can build up in body tissues or crystallize
within joints. See also 
gout; uric acid.
urea 1
A substance that contains nitrogen and is
normally cleared from the blood by the kidney and
excreted via the urine. Diseases that compromise
the function of the kidney often lead to increased
blood levels of urea, which can be measured by the
blood urea nitrogen (BUN) test. See also 
uremia.
2
A synthetic chemical that may be used to remove
fluid from body tissues or the skin.
urea breath test
A procedure for diagnosing the
presence or absence of the bacterium Helicobacter
pylori in the upper gastrointestinal tract, which
causes ulcers. Abbreviated UBT. UBT may be used to
demonstrate that H. pylori has been eliminated by
treatment with antibiotics. UBT is based on the abil-
ity of H. pylori to break down urea, which is nor-
mally produced by the body in the presence of
excess nitrogen and is then eliminated in the urine.
uremia
The presence of an excessive amount of
urea in the blood. Uremia may be a sign of kidney
disease or even kidney failure. See also 
urea.
ureter
One of the two tubes that carry urine from
the kidneys to the bladder. Each ureter arises from
a kidney, descends, and ends in the bladder.
urethra
The tube that leads from the bladder and
transports and discharges urine outside the body. In
males, the urethra travels through the penis and car-
ries semen as well as urine. In females, the urethra
is shorter than in the male, and it emerges above the
vaginal opening.