INTRODUCTION The amino acid obtained from dietary source or body protein turnover is utilised for protein biosynthesis and the production of a wide range nitrogen-containing compounds (creatine, amines, phorphyrin, and so on). The amino parts of amino acid are utilised for the biosynthesis of urea; the remaining carbon skeletons are converted to various intermediates of…

Animals which excrete urea as the major excretory product are said to be ureotelic. Urea is a useful product for a semi-terrestrial animal that is not exposed to scarcity of water but is not necessarily surrounded by large quantities of it. It is, therefore, the main product of some earthworms, shore gastropods, adult amphibians, and…

Animals which excrete their nitrogen predominantly in the form of uric acid are called uricotelic. All genuinely terrestrial animals, including insects, terrestrial gastropods, terrestrial reptiles (snakes and lizards), and birds excrete mainly uric acid. Insects and land snails excrete solid pellets of uric acid, whereas reptiles and birds void a thick paste of uric acid…

Animals which excrete their nitrogenous wastes as ammonia are said to be ammonotelic. Excretion of ammonia, which is presumed to be the primitive material, is especially suited to an aquatic habit. Ammonia is highly soluble in water, with which it forms ammonium hydroxide (NH4OH). The latter passes readily across the cell membranes and is dispersed…

In vertebrates, deamination takes place particularly in liver cells, where the excess of amino acid supplied by eaten food is deaminated. Ammonia produced in this way is highly toxic and must be disposed of. Elimination oft en occurs in the form of uncharged ammonia or a more complex nitrogenous substance, which is either uric acid…