therefore the more kinks, the more beneficial it is to
human health. The kinks, by completely changing the
physical and chemical properties, allow it to form
essential protein associations more easily, disperse
more saturated fatty acids, and interact with water or
blood.
See alsoSATURATED FATTY ACID.
urea A nitrogen-containing waste product; a result of
thenormal breakdown of protein in the liver in mam-
mals. It is created in liver cells from ammonia and car-
bon dioxide, and carried via the bloodstream to the
kidneys, where it is excreted in the urine along with
nitrogen. Urea accumulates in the body of people with
renal failure. Urea is also a synthetic source of nitrogen
made from natural gas.
urease Anickel ENZYME, urea amidohydrolase, that
catalyzes the HYDROLYSISof urea to ammonia and car-
bon dioxide. The ACTIVE SITEcomprises two Ni(II) ions
bridged by a carbamate.
ureter Tubes, about eight to 12 inches in length, that
run from the kidney to the bladder on each side and
carry urine from the kidneys to the bladder.
urethra Anarrow tube or canal that carries urine
from the bladder, and semen from the prostrate and
other sex glands, out via the tip of the penis to the out-
side of the body.
uric acid The end results of urine breakdown, a
product of protein metabolism, which is the major
form of excreting metabolic nitrogen out of the body.
Too much uric acid in the blood and its salts in joints
lead to gout, which causes pain and swelling in the
joints. When urine contains too much uric acid, “kid-
ney” or uric acid stones can develop.
urochordate Achordate (organism having a noto-
chord at some stage of development) without a back-
bone, also called a tunicate or sea squirt; a sessile
marine animal composed of a sack with two siphons in
which water enters and exits, filtered inside by the
sack-shaped body.urticating The act of causing itching or burning sen-
sation to the skin or eyes as a result of being inflicted
by the entry of poison-filled spines (tips often break
off) or setae that contain venom capable of causing
pain and irritation. Found on the abdomen of tarantu-
las, some caterpillars, and the Urticaceae, plants of the
nettle family.334 urea
Colored scanning electron micrograph (SEM) of crystals of calci-
um carbonate on the surface of an otolith, found in the utricle. An
otolith or otoconium is a calcified stone that is found in the otolith
organs of the inner ear. They are attached to sensory hairs, and,
when the head tilts, the stones’ movements cause nerve impulses
that allow a sense of balance and orientation to be maintained. In
humans, otoconia range from 3 to 30 microns (millionths of a
meter) across. Magnification unknown.(Courtesy © Susumu
Nishinaga/Photo Researchers, Inc.)