Maintenance of the cellular water balance is fundamental for life. All cells, even those in multicellular organisms with an organism‐wide osmoregulation, have the ability to actively control their water balance. Osmoregulation encompasses homeostatic processes that maintain an appropriate intracellular environment for biochemical processes as well as turgor of cells and organism. In the laboratory, the osmoregulatory system is studied most conveniently as a response to osmotic shock, causing rapid and dramatic changes in the extracellular water activity. Those rapid changes mediate either water efflux (hyperosmotic shock), and hence cell shrinkage, or influx (hypoosmotic shock), causing cell swelling. The yeast S. cerevisiae, as a free‐living organism experiencing both slow and rapid changes in extracellular water activity, has proven a suitable and genetically tractable experimental system in studying the underlying signaling pathways and regulatory processes governing osmoregulation. Although far from complete, the present picture of yeast osmoregulation is both extensive and detailed (de Nadal et al., 2002; Hohmann, 2002; Klipp et al., 2005). Simulations using mathematical models combined with time course measurements of different molecular processes in signaling and adaptation have allowed elucidation of the first system properties on the yeast osmoregulatory network. Show
View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/S0076687907280024 Overview of Kidney Function and StructureJosephine P. Briggs, ... Jurgen B. Schnermann, in National Kidney Foundation Primer on Kidney Diseases (Sixth Edition), 2014 Comparison Between Volume Regulation and OsmoregulationOsmoregulation is under the control of a single hormonal system, ADH, whereas volume regulation is under the control of a set of redundant and overlapping control mechanisms. Lack or excess of ADH results in defined and rather dramatic clinical syndromes of excess water loss or water retention. In contrast, a defect in a single volume regulatory mechanism generally results in more subtle abnormalities because of the redundant regulatory capacity from the other mechanisms. Therefore, excess aldosterone results in a mild volume retention followed by escape and return to normal Na+ excretion, due to the action of the other mechanisms. Similarly, excess ANP produces only a modest decrement in volume, with no persistent abnormality in Na+ excretion. Severe salt-retaining states, such as liver cirrhosis or congestive heart failure, are characterized by activation of all the volume regulatory mechanisms. Finally, the symptoms that are characteristic of disorders of osmoregulation and of volume regulation are different, with hyponatremia and hypernatremia being the hallmarks of deranged osmoregulation, and edema or hypovolemia resulting from deranged volume regulation. Plasma Na+ concentration does not correlate at all with total body sodium or the extracellular fluid volume. In fact, a low serum Na+ may be found both in sodium excess and sodium deficiency states. However, plasma Na+ concentration is the principal determinant of extracellular fluid osmolarity. In general, abnormalities in Na+ concentration arise from defects in osmoregulation, not volume regulation. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781455746170000017 Water Balance and Gas ExchangeLaurie J. Vitt, Janalee P. Caldwell, in Herpetology (Fourth Edition), 2013 Osmoregulation—Maintaining HomeostasisOsmoregulation, the control of water and salt balance, presents different challenges to organisms living in fresh water, salt water, and aerial or terrestrial environments (Fig. 6.1). Many structures and organs are involved in osmoregulation, including the skin, gills, digestive tract, cloaca, kidneys, and bladder. In fresh water, an amphibian or reptile is hyperosmotic. The ionic concentration of the body is greater than that of the environment, and, if not regulated, water moves in, cells swell and possibly burst, and ions become too dilute. Excessive hydration can be avoided in several ways. Permeability of the skin can be decreased or urinary output can be increased, although salts must be conserved. Marine or brackish species face the opposite challenge. They are hyposmotic in relation to their environment. The ionic concentration of the body is less than that of the environment; thus, water moves out if unregulated, causing dehydration and a concentration of salts in the body fluid. Dehydration can be circumvented by decreasing permeability of skin and reducing the amount of water in urine, although nitrogenous waste must still be removed before reaching toxic levels. Terrestrial species are also at risk of dehydration, but from evaporation rather than osmotic loss of water. They counteract this problem physiologically in a manner similar to marine species. The basic physics of water loss and gain is rather simple, but the mechanisms by which amphibians and reptiles accomplish osmoregulation are varied and often complex (Fig. 6.2).  FIGURE 6.1. Osmotic challenges of amphibians and reptiles in salt water, fresh water, and on land. In salt water, the animal is hyposmotic compared to its environment, and because its internal ion concentration is less than that of the surrounding environment (internal < external), water moves outward. In fresh water, the animal is hyperosmotic to its environment, and the greater internal ion concentration (internal > external) causes water to move inward. On land, the animal is a container of water and ions, but because the animal is not in an aqueous environment, internal fluctuations in ionic balance result from water loss to the relatively drier environment. The animal actually has much higher ion concentrations (internal > external) than surrounding air, and if ionic concentrations reach high levels, as they do in some desert reptiles, ion transfer can occur via salt glands, usually in the nasal or lacrimal region. FIGURE 6.2. Model depicting how transfer of water occurs in cells based on a freshwater system. Water moves by the process of osmosis across the semipermeable membrane of the cell. The direction of water movement depends upon ionic gradients. If ion concentrations are higher inside the cell than outside (as in this example), then water moves in to balance concentration of ions. Semipermeable membranes do not allow all molecules to pass through. Rather, some do and some do not. In addition, cells are capable of actively transporting molecules across membranes. Amphibians and reptiles use a variety of behavioral and physiological mechanisms to maintain water and ionic balance because few natural environments are isotonic with their body fluids. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B978012386919700006X OSMOTIC, IONIC AND NITROGENOUS-WASTE BALANCE | Water Balance and AquaporinC.P. Cutler, in Encyclopedia of Fish Physiology, 2011 Osmoregulation is, generally speaking, the regulation of the internal osmotic environment. In fish, this has many physiological and/or biochemical components. Physiologically, this would include the control of (1) the permeability of the gills to ions and water, (2) the rate of drinking and water and ion intake from the diet, and (3) the loss of ions and or water from urine production. These together control the osmolality (osmotic concentration) and overall volume of body fluids and produce osmotic homeostasis (maintaining the osmolality of body fluids at a constant level). Biochemically, this would include the net effect of water gain or loss and ion excretion or absorption processes across the gills. Ion absorption in the esophagus. Ion and water absorption or secretion in the intestine and kidney, and water absorption in the urinary bladder. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780123745538002148 OSMOTIC, IONIC AND NITROGENOUS-WASTE BALANCE | Osmoregulation in Fishes: An IntroductionD.H. Evans, in Encyclopedia of Fish Physiology, 2011 IntroductionOsmoregulation is a fundamental process of living systems, equivalent in importance to respiration, digestion, or reproduction. Osmoregulatory processes are those that enable a fish to maintain its cellular fluid composition and volume. This is of critical importance because the protein-based processes of cells are sensitive to cytoplasmic ionic concentrations, and cell membranes tolerate relatively small deviations in cell volume (they will either collapse or explode). While terrestrial organisms are continually faced with the problem of dehydration, fishes are surrounded by water, and the water can tend to either dehydrate (in seawater, SW) or hydrate them (in freshwater, FW). The differences in the ionic and total osmotic concentrations of the water and those of the fish body fluids determine the magnitude and the direction of ion (diffusion) and water (osmosis) movements across the fish gill epithelium. Fishes can limit ion and water exchanges by creating barriers at the skin surface (e.g., scales and mucus layers) that limit permeability. However, they still possess gills that are specialized for gas exchange (large surface area, thin, highly vascularized), which remains an excellent site for osmotic movement of ions and water. In fact, when oxygen and carbon dioxide diffusion across the gills increases during activity, ion and water diffusion increases too. This creates a problem for a fish called the osmorespiratory compromise (see also ROLE OF THE GILLS | The Osmorespiratory Compromise). Therefore, post-exercise fish not only have to rectify the depletion of oxygen stores, but they must also deal with ions and water they may have lost or gained as a result of breathing more! When terrestrial animals exercise, they only lose water via their respiratory surface. With the exception of the hagfishes, the ionic concentrations of all fish plasma are intermediate between SW and FW levels (Table 1). Consequently, excluding hagfishes, all fishes must osmoregulate because they usually live in either FW (hyposmotic to fish plasma) or SW (hyperosmotic to fish plasma). Hagfishes are exceptional because their plasma has similar ionic and osmotic concentrations as the SW environment (termed isosmotic), and osmoregulation is not necessary. Animals that maintain their blood plasma isosmotic with the environment are able to save metabolic energy, because life in nonisosmotic solutions requires compensatory transport of solutes and water by cell membranes, epithelial tissues, or specific organs and these processes are energy demanding (variously estimated at 2–8% of resting metabolic rate). Table 1. Ionic compositions of plasma in fishes in SW and FW Salinity or speciesTotal osmolarityaNa+bCl−K+Ca2+Mg2+SO42−UreaTMAOSeawater10504395139.39.65026Hagfish10354865088.25.1123Anadromous lamprey3331561595.63.57.0Euryhaline bull shark10672892965.84.41.837047Dogfish shark11182552416.05.03.00.544172Euryhaline Atlantic stingray953319295330Euryhaline steelhead trout3251531354.01.40.65Euryhaline puffer3631791442.83.11.8Freshwater (soft)1.00.250.230.010.070.040.05Anadromous lamprey11299.62.31.81.5Landlocked lamprey2721201043.92.52.0Euryhaline bull shark5952212204.23.01.315119Euryhaline Atlantic stingray621212209196Freshwater stingray3191781461.22Gar1591334.26.10.3Bowfin2791331101.5Carp2741301252.92.11.2Euryhaline steelhead trout2601531333.81.40.5Euryhaline puffer3461661283.03.51.3 Modified from Evans DH and Claiborne JB (2009) Osmotic and ionic regulation in fishes. In: Evans DH (ed.) Osmotic and Ionic Regulation: Cells and Animals, pp. 295–366. Boca Raton, FL: CRC Press How fluids are regulated inside the body of animals?Osmoregulation is the process of maintenance of salt and water balance (osmotic balance) across membranes within the body's fluids, which are composed of water, plus electrolytes and non-electrolytes. An electrolyte is a solute that dissociates into ions when dissolved in water.
Which of the following process by which an animal regulates its fluid content?Osmoregulation is a process that regulates the osmotic pressure of fluids and electrolytic balance in organisms. In animals, this process is brought about by osmoreceptors, which can detect changes in osmotic pressure. Humans and most other warm-blooded organisms have osmoreceptors in the hypothalamus.
How does the animal body maintain homeostasis?They are adapted to the changes they face in their lifetime through the control system called osmoregulation. Whenever an imbalance occurs, osmoregulation restores the balance by negative feedback. This control system detects the changes and initiates changes to maintain a constant concentration of water in the body.
What is regulation of body fluids in biology?The body requires a particular volume of fluid within it in order to function normally. Most of the fluids which are taken into the body by drinking or eating are excreted by the kidneys to make sure the body does not have too much fluid (fluid over-load) or too little fluid (dehydration).
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