Metabolic Waste - Nitrogen Wastes

Nitrogen Wastes

The nitrogen compounds through which the very toxic nitrogen is eliminated from the organism are ammonia, urea and uric acid. All of these substances are product from the protein metabolism.

Ammonia forms with the oxidation of amino groups (NH₂), which are removed from the proteins when they convert into carbohydrates. It is a very toxic substance and only one nitrogen atom is removed with it. A lot of water is needed for the ammonia excretion. Thus, the marine organisms excrete ammonia directly in the water (aminothelic organisms), while the terrestrial (mainly amphibians and mammals) convert ammonia into urea, a process which occurs in the liver and kidney.

Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion. Urea is a protein metabolism product at vertebrates and part of the invertebrates. These organisms are called ureothelic.

Uric acid is a protein metaporposis product of terrestrial invertebrates, birds and diapsids. Such animals are called uricothelic organisms. In humans and anthropoides, this acid is purine metabolism product. Uric acid is less toxic than ammonia or urea; it contains four nitrogen atoms and a small amount of water is needed for its excretion. Out of solute, it precipitates and forms crystals.