Brodsky, William A. Mount Sinai School of Medicine, City University of New York, New York, New York.
Schilb, T. P. Mount Sinai School of Medicine, City University of New York, New York, New York.
Last reviewed:April 2019
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- Biological mechanisms
- Transport processes
- Active transport
- ATP systems
- Ion-pair transport
- Membrane permeability
- Mechanisms of water transport
- Links to Primary Literature
- Additional Readings
Physiological mechanisms for the maintenance of an optimal and constant level of osmotic activity of the fluid within and around cells. Osmoregulatory mechanisms maintain the internal balance between water and dissolved materials in a biological cell or organism under a variety of environmental conditions, enabling osmotic pressure to be adjusted in relation to the surrounding fluid. (Note that osmosis is the selective passage of solvent molecules through a semipermeable membrane from a dilute solution to a more concentrated one.) The mechanisms of osmoregulation are necessary because practically all living cells function in a fluid environment. Isolated unicellular forms, such as paramecia and amebas, are subject to osmoregulatory mechanisms, as are cells that make up tissues in air-breathing terrestrial animals. Thus, the ionic composition and osmotic activity of extracellular fluids have biological significance with respect to survival of the living cells. The fluid environment of simple unicellular forms of life consists of the oceans, lakes, or streams in which the forms are found, whereas that of complex animal forms consists of the fluid media enclosed by the various compartments of the body. In general, osmoregulatory mechanisms are considered to be most favorable for the initiation and maintenance of vital reactions in the cell and for maximal survival and efficient functioning of the entire organism (Fig. 1). See also: Cell (biology); Cell biology; Ion transport; Osmosis; Physiological ecology (animal); Water
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