- Urea
- A nitrogen-containing substance normally cleared from the blood by the kidney into the urine. Diseases that compromise the function of the kidney often lead to increased blood levels of urea, as measured by the blood urea nitrogen (BUN) test. Urea is of major historical significance. It was the first organic chermical compound ever synthesized. The German chemist Friedrich Wöhler in 1828 attempted to make ammonium cyanate from silver cyanide and ammonium chloride and, in the process, accidentally made urea. Wöhler wrote his mentor Jöns Berzelius, "I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea." This pioneering experiment disproved the theory of vitalism, the concept that organic chemicals could only be modified chemically, but that living plants or animals were needed to produce them. Wöhler had also discovered that urea and ammonium cyanate had the same chemical formula but very different chemical properties. This was due to isomerism, the phenomenon in which two or more chemical compounds have the same number and type of atoms but, because those atoms are arranged differently, each compound has different chemical properties.
* * *The chief end product of nitrogen metabolism in mammals, formed in the liver by means of the Krebs-Henseleit cycle and excreted in normal adult human urine in the amount of about 32 g a day (about 67 of the nitrogen excreted from the body). It may be obtained artificially by heating a solution of ammonium cyanate. It occurs as colorless or white prismatic crystals, without odor but with a cooling saline taste, is soluble in water, and forms salts with acids; has been used as a diuretic in kidney function tests, and topically for various dermatitides. [G. ouron, urine]- u. stibamine a u. derivative of stibanilic acid, used in the treatment of kala azar and certain other tropical diseases.
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urea yu̇-'rē-ə n a soluble weakly basic nitrogenous compound CH4N2O that is the chief solid component of mammalian urine and an end product of protein decomposition and that is administered intravenously as a diuretic drug called also carbamide* * *
n.the main breakdown product of protein metabolism. It is the chemical form in which unrequired nitrogen is excreted by the body in the urine. Urea is formed in the liver from ammonia and carbon dioxide in a series of enzyme-mediated reactions (the urea cycle). Accumulation of urea in the bloodstream together with other nitrogenous compounds is due to kidney failure and gives rise to uraemia.* * *
(u-reґə) 1. a compound, CO(NH2)2, formed in the liver via the urea cycle (q.v.) from ammonia produced by the deamination of amino acids and later excreted by the kidney; it is the principal end product of protein catabolism and constitutes about one half of the total urinary solids. Elevation of the blood levels of urea and other nitrogenous compounds (azotemia) occurs with decreased glomerular filtration rate due to inadequate renal perfusion, acute or chronic renal disease, or urinary tract obstruction (see uremia). Called also carbamide. 2. [USP] a preparation of urea administered intravenously as an osmotic diuretic to reduce intracranial or intraocular pressure; injected transabdominally into the amniotic sac as a hypertonic solution to induce abortion of a second trimester pregnancy, and used in topical preparations to moisten and soften rough dry skin. 3. a preparation of urea used as a feed additive for ruminants, enhancing protein synthesis from dietary roughage and stimulating multiplication of microorganisms that digest cellulose.
Medical dictionary. 2011.
