unsaturated fat A fat that is liquid at room temperature and comes from a plant, such as olive, peanut, corn, cottonseed, sunflower, safflower, or soybean oil. Unsaturated fat tends not to raise the level of LDL (“bad”) cholesterol in the blood.
unsteadiness Loss of one’s equilibrium in respect to the environment, often with a feeling of almost falling and often as a result of bumping into something. There are many causes for unsteadiness, including problems in the cerebral or cerebellar portions of the brain, the spinal cord, vestibular system, or inner ear. See also dizziness; lightheadedness;…
upper GI series A series of X-rays of the upper 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.
urachus A canal that connects the urinary bladder to the umbilicus (bellybutton) during fetal development. The urachus is normally obliterated, 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…
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…
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 ability of H. pylori to break down urea,…
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 carries semen as well as urine. In females, the urethra is shorter than in the male, and it emerges above the vaginal opening.
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 bladder to enter the urethra. This sphincter cannot be willfully…