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.
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 lotions.
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.
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