Excretion

Article By:

Martin, Arthur W. Department of Zoology, University of Washington, Seattle, Washington.

Last reviewed:September 2021

DOI:https://doi.org/10.1036/1097-8542.248300

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• Excretion, published January 2020:Download PDF Get Adobe Acrobat Reader

The removal of excess material from a cell or a living organism. Excretion is the process by which organisms, chiefly animals, eliminate metabolic waste products and excess water. In general, the concept of excretion is quite broad. Therefore, the study of excretion is most often limited to the animal kingdom (Fig. 1). (Because of differences in physiology, excretion is not a major problem in the plant kingdom.) In addition, certain biological processes that could fall under the heading of excretion are typically studied together with other physiological mechanisms. For example, carbon dioxide is one of the chief products of the metabolism of cells, and special mechanisms have evolved in large animals for the transport of carbon dioxide in blood. However, the removal of carbon dioxide is considered to be a process of blood-gas transport. Similarly, the excretion of heat is studied as a mechanism of body-temperature regulation, whereas the excretion of salts is viewed as an osmoregulatory process. See also: Animal; Animal kingdom; Carbon dioxide; Osmoregulatory mechanisms; Respiration; Thermoregulation

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