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Which waste products are produced during animal metabolism?

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During animal metabolism, the body produces several waste products that must be eliminated to maintain internal balance. These substances are primarily generated through the breakdown of food molecules and the regulation of body fluids.12

Nitrogenous Waste

The primary nitrogenous by-products arise from the metabolism of amino acids, which are derived from proteins. Depending on the animal's environment and water-conservation needs, these are excreted in different forms:1
* Ammonia: A highly toxic but water-soluble gas excreted by many small aquatic animals.13
* Urea: A less harmful, water-soluble compound produced by mammals and some amphibians and fishes.13
* Uric acid: A highly insoluble substance excreted as a thick suspension or dry powder by birds, reptiles, and terrestrial insects.13

Other Metabolic By-products

In addition to nitrogenous compounds, cellular processes such as cellular respiration produce:
* Carbon dioxide: A by-product of the tricarboxylic acid cycle and general respiration.45
* Water: Produced during the final stages of oxidative phosphorylation.5

The kidneys also facilitate the removal of other metabolic materials, including creatinine, inorganic salts, and various pigmented products of blood breakdown.23