ureotelic

Ureotelic is a term used in physiology and biochemistry to describe organisms that excrete most of their nitrogenous waste as urea rather than as ammonia or uric acid. Ureotelism is typical of many adult mammals, including humans, and some amphibians. It stands in contrast to ammonotelic organisms, which excrete ammonia, and uricotelic organisms, which excrete uric acid.

In vertebrates, urea production occurs mainly in the liver through the urea cycle (also called the ornithine cycle). Ammonia, generated from amino acid breakdown, is converted into urea, a less toxic compound. Urea is then released into the bloodstream, transported to the kidneys, and excreted in urine. This pathway allows nitrogen disposal with relatively moderate water loss compared with ammonotelic excretion, while still incurring a substantial energy cost to synthesize urea.

Ecological and evolutionary considerations help explain ureotelism. It provides a balance between toxic waste management and water conservation, making it advantageous for many terrestrial and semi-terrestrial organisms. By contrast, uricotelism, common in birds and many reptiles, further minimizes water loss but requires more energy to synthesize uric acid. Ammonotelism is typical of many aquatic organisms, which can afford to release highly soluble ammonia directly into the surrounding water.

In medical and physiological contexts, ureotelic metabolism is often studied in relation to the urea cycle, kidney function, and disorders affecting nitrogen balance.