Urea

Urea is a compound with the chemical formula (NH2)2CO. It is a nitrogenous compound containing a carbonyl group attached to two amine groups with osmotic diuretic activity. In vivo, urea is formed in the liver via the urea cycle from ammonia and is the final end product of protein metabolism. Administration of urea elevates blood plasma osmolality, resulting in enhanced flow of water from tissues, including the brain, cerebrospinal fluid and eye, into interstitial fluid and plasma, thereby decreasing pressure in those tissues and increasing urine output.

Chemical Structure

Urea is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline. The body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two ammonia molecules (NH3) with a carbon dioxide (CO2) molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen (N) and is an important raw material for the chemical industry.

Biological Role

In humans, urea is formed in the liver through the Urea Cycle, which is an organic cycle. The cycle involves the production of urea from ammonia, carbon dioxide, aspartate, and water. The cycle was the first metabolic cycle to be discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the TCA cycle. For this discovery, Hans Krebs received the Nobel Prize in Physiology or Medicine in 1953.

Clinical Significance

Urea levels in the blood can indicate a variety of conditions. High levels, or hyperuremia, can indicate kidney dysfunction, dehydration, shock, or high protein intake. Low levels, or hypouremia, can indicate liver disease or malnutrition. Urea is also used in a variety of diagnostic tests, including the urea breath test, which can detect the presence of Helicobacter pylori bacteria in the stomach.

See Also

• Urea Cycle
• Urea Breath Test
• Hyperuremia
• Hypouremia

References

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