ornithine cycleor urea cycle
ornithine cycleor urea cyclea circular biochemical pathway in the liver cells of mammals, with three major steps, in which excess ammonia, produced from the breakdown of amino acids, and carbon dioxide react together to give UREA which is filtered out by the kidneys and excreted. The reaction is essentially:
See Fig. 237 . The cycle is found in other land vertebrates but not birds or reptiles.