Osmoregulation by Vertebrates in Aquatic Environments

Abstract

Because the salt concentration of the body fluids of aquatic vertebrates differs from that of their freshwater or marine environment, they face net movements of water and salt across their permeable membranes, most notably the gill. Various organs and transport processes are involved in maintaining internal consistency in the face of these potential osmotic and salt problems.

Keywords: osmoregulation; vertebrates; fishes; amphibians; reptiles; birds; mammals

Figure 1.

Osmoregulationin a freshwater fish. The net osmotic gain of water and diffusional loss ofsalt across the gills is balanced by excretion of relatively dilute urine,active uptake of salt across the gill, and possibly some ingestion of salt inthe food. Blue arrows represent passive movements of salt and water, and redarrows indicate active pathways of osmoregulation. See text for details.Outline drawing of a goldfish was redrawn from Greenwood HP, et al.(1966) Bulletin of the American Museum of Natural History 131:339–456.

Figure 2.

Osmoregulationby a marine teleost fish. The net osmotic loss of water and diffusional gainof salt across the gills is balanced by ingestion of sea water, production ofsmall volumes of urine that contains some salt, and active extrusion of saltacross the gill. Blue arrows represent passive movements of salt and water,and red arrows indicate active pathways of osmoregulation. See text fordetails. Outline drawing of a tuna was redrawn from Bigelow HB and SchroederWS (1953) Fisheries Bulletin, Fish and Wildlife Service 53:1–577.

Figure 3.

Osmoregulationby a shark. The osmotic gain of water and diffusional gain of salt across thegills is balanced by production of large volumes of urine that contains somesalt, active secretion of salt via the rectal gland, and possibly activeextrusion of salt across the gill. Blue arrows represent passive movements ofsalt and water, and red arrows indicate active pathways of osmoregulation. Seetext for details. Outline drawing of a spiny dogfish shark was redrawn fromBigelow HB and Schroeder WS (1953) Fisheries Bulletin, Fish and WildlifeService 53: 1–577.

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Further Reading

Campbell NA and Reece JB (2002) Biology, 6th edn. San Francisco: Benjamin Cummings.

Evans DH (1998) The Physiology of Fishes, 2nd edn. Boca Raton: CRC Press.

Goldstein L (1999) Comparative physiology of osmoregulation: The legacies of August Krogh and Homer Smith. Journal of Experimental Zoology 283: 619–733.

NcNab BK (2002) The Physiological Ecology of Vertebrates. A View from Energetics. Ithaca: Comstock Publishing Associates.

Randall D, Burggren W and French K (2002) Animal Physiology. Mechanisms and Adaptations, 5th edn. New York: WH Freeman.

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How to Cite close
Evans, David H(Mar 2003) Osmoregulation by Vertebrates in Aquatic Environments. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001842]