Urea is an organic compound of carbon, nitrogen, oxygen
and hydrogen, with the formula CON2H4 and the structure
Humans produce urea from carbon dioxide and
ammonia in the urea cycle, an anabolic process. This
expenditure of energy is necessary because ammonia, a
common metabolic waste product, is toxic and must be
neutralized. Aquatic animals do not produce urea; living
in an abundant supply of water, they can simply excrete
ammonia immediately as it is produced. Birds, with more
severe restrictions on water consumption than most other
terrestrial creatures, produce uric acid, a compound even
less toxic than urea.
Because urea is produced and excreted at a roughly
constant rate, high levels of urea in the blood indicate a
problem with the removal, or more rarely with the
over-production, of urea in the body.
The most common cause of uremia is renal problems. It is
measured along with creatinine to indicate direct problems
with the kidneys (e.g. chronic renal failure) or secondary
problems such as hypothyroidism.
Urea levels can also be increased in some malignant blood
disorders, (e.g. leukaemia and multiple myeloma).
Markedly high levels of urea (uremia) can cause
neurological disturbances. Prolonged periods of uremia may
result in the skin taking on a grey discoloration.
If possible, the patient should avoid eating a diet high in meat
or other protein before having a blood urea nitrogen (BUN) test.
Urea was discovered by Hilaire Rouelle in 1773. It was the
first organic compound to be artificially synthesised in
1828 by Friedrich Woehler, who prepared it by the reaction
of potassium cyanate with ammonium sulfate. This disproved
the theory that the chemicals of living organisms are
substantially different from inanimate matter and started
the discipline of organic chemistry.
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Its principal industrial use is the manufacture of
plastics (specifically, urea-formaldehyde resin).
It is also a component of many fertilisers, providing a
nitrogen source that is necessary for plants.
It can also be found in some hair conditioners and
Urea is a powerful protein denaturant. This property can
be exploited to help solubilize proteins that do not go
into solution easily. For this application it is used in
concentrations up to 6M.