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Zoology the adjustment of the osmotic pressure of a cell or organism in relation to the surrounding fluid
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the set of physicochemical and physiological processes that maintain the osmotic pressure of the intercellular fluids, lymph, and blood at a constant level in homoiosmotic animals.

Osmoregulation is found in organisms that inhabit environments with varying concentrations of osmotically active substances, chiefly salts, and in organisms whose level of water and salt utilization vary. Characteristic of all freshwater and terrestrial animals, it is also exhibited by some crustaceans and by all marine vertebrates, except members of the subclass Myxini. Its physiological mechanism is a reflex by which a change in osmotic pressure of the blood or intercellular fluid is perceived by osmoreceptors, which transmit impulses to the nerve centers that regulate the consumption and excretion of water and salts by the osmoregulatory organs, for example, the nephridia, kidneys, and salt glands.

Osmoregulation is hyperosmotic when the osmotic pressure of the internal medium is greater than that of the fluid of the environment and hypoosmotic when the internal osmotic pressure is less. In hyperosmotic regulation, the excess water is excreted by animals mainly through the kidneys and by plants through the stomata; in hypoosmotic regulation, animals replenish the water that is lost through the skin by drinking water that is rich in salts and by excreting the excess salt chiefly through the salt glands.

Osmoregulation in all freshwater animals and marine chondrichthians is hyperosmotic. In sharks and members of the suborder Batoidei, the need for hyperosmotic regulation is due to the high concentration of urea in the blood, and water enters the body across the osmotic gradient of the water-permeable portions of the teguments. In all animals, excess water is excreted by the kidneys or their analogs—the contractile vacuoles of protozoans and the nephridia; salts are absorbed from freshwater by the gills or—in amphibians—by the skin.

Organisms that lose water in the urine and through the integuments exhibit hypoosmotic regulation: these include marine teleosts and marine reptiles. To compensate for the loss, they drink seawater, which is freshened by their salt glands and other organs that excrete concentrated salt solutions. The main organ of osmoregulation in mammals in the kidney, which can excrete hypotonic urine when water is in excess and hypertonic urine when water is scarce. Migratory fish, for example, salmon, and some crustaceans exhibit both hyperosmotic and hypoosmotic osmoregulation and consequently can live in both freshwater and seawater.

In poikilosmotic animals—marine mollusks and echinoderms—the osmotic pressure of the blood varies with the osmotic pressure of the environment. Osmoregulation in these animals is cellular: when the osmotic pressure of the blood increases, the concentration of organic substances in the cells, mainly amino acids, to which the cell membrane is slightly permeable increases by the same amount. As a result, the salt concentration and water content of the cell do not change, and the osmotic pressure is equalized by the accumulation of osmotically active substances. A decrease in the osmotic pressures of the blood and environment decreases the concentration of organic substances in the cells. Thus, cellular osmoregulation provides for the limited adaptation of poikilosmotic animals to fluctuations of osmotic pressure in the environment.




The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Leaf conductance and osmoregulation of field grown sorghum genotypes.
The SON is involved in regulating diverse physiologic functions including osmoregulation, blood pressure regulation, parturition, and lactation [reviewed by Higuchi and Okere (2002)].
The fish manages this by urinating around 30pc of its body weight each day, as its highly efficient kidneys remove the mineral salt - this is what is meant by osmoregulation.
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Three osmoregulation experiments were conducted on the estuarine clam Rangia cuneata (Gray) to determine if the lack of ability to osmoregulate could have been responsible for observed mortalities during previous laboratory exposures (McConnell & Harrel 1995) to non-lethal concentrations of copper (20-25 [micro]g/L).
This is the first study to our knowledge that has investigated physiological osmoregulation in such a large group of healthy, non-hospitalized elderly subjects.
These morphological effects, even due to low concentrations of metals, can functionally affect fundamental processes such as osmoregulation and antioxidant defense in gills (Puerto et al., 2010).
Different from the soluble sugars, the increase in total amino acids concentration with increasing salinity was greater than that of the other organic solutes, however, this increase was not enough to show its capacity of osmoregulation in leaf cells; thus, its function may be linked to the protection of cellular structures (Munns, 2005).
Using this assembly, we generated a curated list of candidate genes potentially subject to strong natural selection, including genes associated with osmoregulation, oxygen binding and delivery, and other aspects of marine life.
(2015) reported the de novo assembly of the blue crab transcriptome, which identified thousands of genes with functions (gene ontology assignments) related to processing xenobiotic compounds, defense, hypoxia, osmoregulation, and ecdysis, among many others.
Moreover free amino acids promote the uptake of K+ and Ca+ thereby helping in osmoregulation through inorganic solutes (Navari-Izzo et al., 1990).
The interaction of genes involved in osmoregulation, stress responsive transcription factors, and other metabolic pathways mentioned in the following discussion revealed that HKI1532 was better adapted to water stress at a lower rate of photosynthesis in order to maintain the crucial biological functions.