Osmoregulation

9 Key excerpts on "Osmoregulation"

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  Nutritional Biochemistry

  From the Classroom to the Research Bench

  • Sami Dridi(Author)
  • 2022(Publication Date)
  • Bentham Science Publishers

    (Publisher)

  As I stated in Chapter 1, we drink because we are thirsty. Water is the most abundant constituent (50-60% of body weight) in the body. Approximately 55-75% of total body water is in the intracellular compartment, and the rest (~25-45%) in the extracellular compartment with a ratio of 1:3 intravascular (plasma) and extravascular (interstitial) spaces. Animals and humans continuously lose water by various physiological and cellular processes, including sweating, urination, and basal metabolic activity. To maintain water homeostasis and compensate for such losses, animals must drink sufficient water and ingest food from external sources. The maintenance of this in-and-out water balance represents a key homeostatic function for survival in all organisms. It specifically occurs through a balance between water intake/excretion and salt intake/excretion to keep the osmolality of the extracellular fluid at the optimal set-point. These processes are finely and tightly controlled at the entire organism level, including the peripheral sensory system and the central neural circuits. This chapter highlights recent advances in the field and describes the molecular mechanisms involved in the regulation of body fluid homeostasis.

  6.1. Organs Involved in Osmoregulation

  Based on the Encyclopaedia, Osmoregulation is the maintenance by an organism of an internal balance between water and dissolved materials regardless of environmental conditions. As water and sodium are associated (where goes sodium, water soon follows whether by osmosis1 or bolus flows), all organisms have to regulate sodium and water in order to remain in homeostasis. Several organs, depending on vertebrate species, are involved in Osmoregulation to inhabit a wide variety of environments. With the exception of the mammals where the only kidney is involved, all other vertebrates use more than one organ/system to maintain the osmoregulatory homeostasis. Birds, for instance, use kidney, intestine, and salt glands for the maintenance of fluid and electrolyte balance. Reptiles utilize the kidney, intestine, bladder, and salt glands. Fish employ kidneys, intestine, bladder, and gills. In addition to the skin, amphibians make use of the same organs as fish. It is noteworthy that mammals can lose water and electrolytes via various routes, including skin, lungs, GI, but not for Osmoregulation. The mammalian urinary bladder is a urine storage organ and is not involved in Osmoregulation [1 ].

  Changes in body water/sodium balance disturb the extracellular fluid volume, which in turn affects arterial blood pressure. The CNS receives continuous inputs from the peripheral organs about the status of ECF osmolality, sodium concentration, sense of taste, fluid volume, and blood pressure, and acts accordingly to adjust the body fluid homeostasis.

  6.2. Water and Sodium Taste

  The question that one might ask is whether water has a taste receptor or not. In Drosophila, water taste is mediated by ppk28, a member of the epithelial sodium channel/degenerin (ENac/Deg) family, which is expressed in gustatory receptor neurons [2 , 3 ]. In fact, functional studies showed that water consumption was reduced in flies lacking ppk28 [4 ]. In mammals, however, data are not conclusive, although electrophysiological studies have shown that water can stimulate taste nerves in several species, including cats and dogs [5 ]. Recent study showed that water and sour (acid) tastes are encoded by the same taste receptor cells [6 ]. Zocchi et al. [6

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  Marine Mammal Physiology

  Requisites for Ocean Living

  • Michael A. Castellini, Jo-Ann Mellish, Michael A. Castellini, Jo-Ann Mellish(Authors)
  • 2015(Publication Date)
  • CRC Press

    (Publisher)

  The evolved physiologi-cal mechanisms have allowed marine mammals to conserve salts and water during pro-longed fasting as well with virtually no consequences. In this chapter, the osmoregulatory mechanisms in marine mammals are reviewed. 7.2 Knowledge 7.2.1 Constancy of internal environment When solutions with different solute concentrations are separated by a semi-permeable membrane, water molecules will move down their concentration gradient (from the com-partment with the lower concentration of dissolved particles to the compartment with the greater concentration) through the membrane until the concentrations of the two compart-ments are equal, or reach an osmotic equilibrium. The process is defined as osmosis , and the power of the solution to draw water through the membrane is referred to as osmotic pressure . The osmolality of the plasma, therefore, is determined by the sum total of all the dissolved particles in a solution (water) such as electrolytes, glucose, and urea (blood urea nitrogen, BUN) and can be approximated by the following formula: Plasma osmolality Na mEq/l 2 glucose mg/dl BUN (mg/dl) = * + + ( ) ( ) . 18 2 8 Because the concentrations of electrolytes, especially sodium, potassiums, and chloride, in plasma are rigidly controlled so is the osmolality. The maintenance of plasma constitu-ents within defined ranges suitable for cellular activity represents the homeostatic control afforded by adaptable osmoregulatory mechanisms. Aside from the potential impacts of the environment on plasma osmolality, diet and prolonged fasting can also contribute to alterations in osmolality. For example, protein loading from protein-rich diets can influ-ence plasma urea concentration, which would be reflected by an increase in plasma osmo-lality. Plasma osmolality in humans ranges from 275 to 290 mOsm/kg; however, those in marine mammals are comparatively higher (Table 7.1).

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  Biological Psychology

  • James Kalat(Author)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Osmotic pressure occurs when solutes are more concentrated on one side of the membrane than on the other. If you eat something salty, sodium ions spread through the blood and the extracellular fluid but do not cross the membranes into cells. The result is a higher concentration of solutes (including sodium) outside the cells than inside. The resulting osmotic pressure draws water from the cells into the extracellular fluid. Certain neurons detect their own loss of water and then trigger osmotic thirst , a drive for water that W ater constitutes about 70 percent of the mammalian body. Because the concentration of chemicals in water determines the rate of all chemical reactions in the body, you need to maintain the water in your body within narrow limits. The body also needs enough fluid in the circulatory system to maintain normal blood pressure. You could survive for days, maybe weeks, without food, but not long without water. Mechanisms of Water Regulation Species differ in their strategies for maintaining water. Beavers and other animals that live in rivers or lakes drink plenty of water, eat moist foods, and excrete dilute urine. In contrast, most gerbils and other desert animals go through life without drinking at all. They gain water from their food and they have many adaptations to avoid losing water, including the ability to excrete dry feces and concentrated urine. Unable to sweat, they avoid the heat of the day by burrowing under the ground. Their highly convoluted nasal passages minimize water loss when they exhale. We humans vary our strategy depending on circum-stances. If you cannot find enough to drink or if the water tastes bad, you conserve water by excreting more concentrated urine and decreasing your sweat, somewhat like a gerbil, although not to the same extreme. Your posterior pituitary (see Figure 9.6) releases the hormone vasopressin that raises blood pressure by constricting blood vessels.

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  Principles of Biology: Animal Systems: A Tutorial Study Guide (box set)

  • Nicoladie Tam(Author)
  • 0(Publication Date)
  • Nicoladie Tam, Ph.D.

    (Publisher)

  The renal system is evolved from simple regulation of osmosis to regulation of fluid and mineral balance, such that the concentration of various ions in the body is maintained (and kept at a constant level). Maintaining a constant concentration of the internal environment is essential for cellular functions.

  Why is Osmoregulation important for aquatic animals? Osmoregulation is particularly important for aquatic animals, since the animal will shrink or swell depending on the osmolality of the animal relative to the external osmolality Osmoregulation is less important in terrestrial animal, although osmolality still needs to be maintained for cellular function, otherwise bloating can occur. What is the primary organ of the renal system in vertebrates? Kidney is the major organ that regulates the fluid balance and filtration. The kidney contains functional units called nephrons for filtration, reabsorption and maintaining fluid balance. Why is it important to have to kidney to survive?

  It is because without the homeostatic regulation of bodily fluid, osmosis and filtration of materials such as toxins, the fluid concentration will go out of balance, and toxins will build up in the system.

  When the kidneys fail, a dialysis machine can be used to filter the blood as a temporary method to remove the toxins from the blood, and maintain the fluid and osmotic balance. However, the filtration capability of a dialysis machine is not as good as the kidneys, and transplant of kidney is required for long-term maintenance.

  What are the primary functions of the kidney? It filters blood, regulates the osmolality, water and ionic balance, reabsorb essential materials, and eliminate nitrogen wastes and other unwanted materials.

  Kidney performs these functions by filtering out most materials (even essential nutrients) from the blood except for large cells such as red blood cells and white blood cells. It then reabsorbs the essential materials (including water, nutrients, minerals, etc.), and discards the rest of the materials (including toxins, drugs, nitrogen wastes, etc.)

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  Internal Anatomy and Physiological Regulation

  • Linda Mantel(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  B . Limiting M e c h a n i s m s — O s m o c o n f o r m i t y O n e of the most direct means of minimizing the diffusive movements of ions and water is to reduce the concentration and osmotic gradients be-tween the blood and the external medium. This pattern, partial or complete osmoconformity, is widely exhibited in marine and brackish-water crustaceans. Osmoconformers reduce the osmotic gradient by decreasing osmolality of hemolymph w h e n in dilute seawater. H o w e v e r , this decrease presents the same problem to internal tissues that changes in external concentration present to hemolymph—influx of water followed by swelling. Osmoconfor-mers regulate the v o l u m e of their tissues by decreasing intracellular con-centration of osmotically active solutes, mainly by changes in content of free amino acids in tissues (Schoffeniels and Gilles, 1970). The ultimate range of viability in osmoconformers may be determined by the ability of their tissues to make these adjustments. Indeed, complete osmoconformers are not found in fresh water—the metabolic requirements of tissues for solutes are such that blood must be maintained more concentrated than a freshwater milieu. C . Compensatory M e c h a n i s m s — O s m o r e g u l a t i o n By maintaining a hyperosmotic internal concentration w h e n in a dilute medium, osmoregulators place less of a burden on their internal tissues. H o w e v e r , the problem of osmotic influx of water remains and can be over-c o m e by reducing permeability to water, increasing efflux of water via the urine, and increasing uptake of salts from the dilute medium. W a t e r gained osmotically can be lost either by production of an equal volume of urine isosmotic to h e m o l y m p h , or by production of a urine hypoosmotic to hemo-lymph, w h i c h also reduces loss of salt. Both of these mechanisms are used, but the former is more c o m m o n .

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  Integrated Endocrinology

  • John Laycock, Karim Meeran(Authors)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  Chapter 12 The Endocrine Control of Salt and Water Balance

  Introduction

  Land animals have evolved over millions of years from an aquatic past when the surrounding medium was a saline solution, namely, the sea. The sea nowadays has a salinity of approximately 3.5% (i.e. 35 g.L−1 ) or, given a molecular weight of 58.5 for NaCl, a molarity of approximately 600 mMol.L−1 . This is considerably more hypertonic than our own internal environment, the extracellular fluid, which has an approximate molarity of 150 mMol.L−1 . That evolutionary process has involved the development of various mechanisms which have allowed these animals, including humans, to survive in a very different, essentially dry, environment. For example, our bodies are protected by an impermeable skin allowing us to retain water, which we normally imbibe in a controlled manner, and our cells have developed mechanisms which maintain an intracellular environment suitable to allow vital enzyme-catalysed reactions to take place in order to sustain life. Central to these mechanisms is the appreciation that water moves across cell membranes up an osmotic gradient so that the regulation of osmotically active particles is essential to the maintenance of that internal environment. With sodium and chloride ions making up almost all the osmotically active particles in the extracellular fluid, giving a normal osmolality of nearly 300 mOsmol.kg−1 of water, the importance of salt regulation becomes apparent.

  Water is essential for life, and represents approximately two-thirds of our body weight (i.e. of the order of 40 L in a 70 kg individual). Of this total volume of water, approximately two-thirds is intracellular with the remainder being extracellular. The extracellular fluid volume (ECFV) itself is comprised mostly of interstitial water (around 10 L) and plasma (around 2.5 L). The maintenance of an intracellular medium compatible with the vital activities of enzyme-driven cellular reactions can be considered to be essentially down to the activity of Na+ –K+

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  Invited Lectures

  Proceedings of the Third Congress of the European Society for Comparative Physiology and Biochemistry, August 31-September 3, 1981, Noordwijkerhout, Netherlands

  • A. D. F. Addink, N. Spronk(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  Jørgensen, C., Skadhauge, E. Osmotic and volume regulation. Copenhagen: Munksgaard, 1978; 512. [A. Benzon symposium XI]. Berridge, M.L., Oschman, J.L. Transporting epithelia. New York, London: Academic Press, 1972; 91. Gilles, R. Métabolisme des acides aminés et contrôle du volume cellulaire. Liège, Belgique: Vaillant-Carmanne, 1974; 167. Gilles, R., Mechanism of ion and OsmoregulationKinne, O., eds. “Marine Ecology”; Vol.2. Wiley, Chichester, New York, 1975:259–347. [part 1]. Gilles, R. Mechanisms of Osmoregulation in animals. Chichester, New York: Wiley, 1979; 667. Gilles, R. Animals and Environmental fitness; 1. Pergamon Press, Oxford, New York, 1980:619. Gupta, B.L., Moreton, R.B., Oschman, J.L., Wall, B.J. Transport of ions and water in animals. New York, London: Academic Press, 1977; 817. Jungreis, A.M., Hodges, T.K., Kleinzeller, A., Schultz, S. Water relations in membrane transport in plants and animals. New York, London: Academic Press, 1977; 393.

  Keynes, R.D. A discussion on active transport of salts and water in living tissues. Phil. Trans. Roy. Soc. Lond. B. 1971; 262:85–342.

  Kregenow, F.M. Osmoregulatory salt transporting mechanisms: control of cell volume in anisosmotic media. Ann. Rev. Physiol. 1981; 43:493–505.

  Krogh, A. Osmotic regulation in aquatic animals. Cambridge: Cambridge University Press, 1939; 242.

  MacKnight, A.D., Leaf, A. Regulation of cellular volume. Physiol. Rev. 1977; 57:510–573.

  Maloiy, G.M. Comparative physiology of Osmoregulation in animals; 1. Academic Press, New-York, London, 1979:677. [Vol. 2. 246 pp]. Potts, W.T., Parry, G. Osmotic and ionic regulation in animals. Oxford, New York: Pergamon Press, 1964; 423.

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  Goals of Ionic Regulation

  R.F. Burton,     Institute of Physiology, University of Glasgow, Glasgow, UK

  Abstract

  The optimum internal environment in vertebrates and molluscs is discussed in relation to electrolyte shifts in hypercapnia, the homeostatic roles of calcium carbonate and hydroxyapatite and the effects of cations on nerve excitability. Patterns of ionic balance may be maintained within individual animals and within groups of related species despite variations in individual ions. These suggest some of the goals. Thus in non-marine Prosobranchia there is, as in vertebrates, a close interrelationship amongst concentrations of potassium, sodium, calcium and magnesium that suggests a constant requirement for excitability. Ionic regulation acts to preserve appropriate ionic balance simultaneously for a variety of physiological functions, but the achievement of one such goal sometimes hinders that of another and this too may have influenced the evolution of homeostasis.

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  Sturkie's Avian Physiology

  • G. Causey Whittow(Author)
  • 1999(Publication Date)
  • Academic Press

    (Publisher)

  Avian Osmoregulation—regulation of the balance of water and electrolytes—involves the interacting contributions of a number of organs and organ systems, including the kidneys, intestinal tract, salt glands (when present), and skin and respiratory tracts (as routes of evaporative water loss). Among these, the kidneys are usually considered the primary organs of regulation. However, the kidneys empty their output into the lower intestine, after which the urine may reside in and be modified by the coprodeum, colon, and ceca; function of the kidney must therefore be integrated with these latter organs. Furthermore, under some circumstances (and in some species) the salt glands subsume a primary osmoregulatory role, and the majority of total water loss may in fact be evaporative, not excretory. The present chapter will focus most heavily on anatomical and functional organization of the kidneys and cloaca, but will also examine the physiology of these other organs of Osmoregulation.

  Before discussing the physiological mechanisms of regulation, it is worth considering the normal physiologic state—what is it that is protected by the osmoregulatory systems. Table 1 provides normal values for several of these variables.

  TABLE 1 Typical Normal Values of Some Regulated Osmoregulatory Variablesa

  Total body water	60–70 ml/100 g body mass
  Extracellular fluid volume	20–25 ml/100 g body mass
  Plasma volume	3.5–6.5 ml/100 g body mass
  Plasma osmolality	320–370 mosmol/kg water
  Plasma Na+	150–170 meq/liter
  Plasma K+	2–5 meq/liter
  Plasma uric acid	0.1–1 mmol/liter

  a Values are typical for adult birds. Data are taken primarily from Skadhauge (1981) , which should be consulted for references to original literature; the ranges presented encompass most of the variability among data compiled in that review.

  III INTAKE OF WATER AND SOLUTES

  A Drinking

  Many birds (especially carnivores and frugivores) routinely acquire all of the water they require through their food; a few species, particularly small, xerophilic birds, can survive on the metabolic water produced from a dry diet even in the absence of drinking water (Bartholomew, 1972)

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  Intensive Care in Nephrology

  • Patrick Murray, Hugh Brady, Jesse B. Hall, Patrick Murray, Hugh Brady, Jesse B. Hall(Authors)
  • 2005(Publication Date)
  • CRC Press

    (Publisher)

  22 Water homeostasis Jerrold S Levine and Rajiv Poduval INTRODUCTION The plasma concentration of sodium, or [Na + ] p , and the plasma osmolality are very closely related measures. The correlation between them is so tight that [Na + ] p is commonly used as a surrogate for plasma osmolality. Indeed, as we shall discuss below, after introducing the concept of effective osmoles, [Na + ] p may be the physiologically more relevant variable. Disturbances in which [Na + ] p is reduced, collectively referred to as hyponatremia, are virtually always accompanied by a reduction of plasma osmolality. Similarly, disturbances in which [Na + ] p is increased, collectively referred to as hypernatremia, are indicative of an elevation of plasma osmolality. Properly understood, both hyponatremia and hypernatremia are not single diseases, but instead syndromes, and each has multiple potential causes. Correct diagnosis and management of these two syndromes depend critically on an understanding of the underlying physiology. In this chapter, using simple physiologic principles, we construct diagnostic algorithms that enable the clinician to identify the responsible disease state(s) and pathophysiologic mechanism(s). We then use these same physiologic principles to devise a treatment strategy that is based solely on quantitative analysis of the daily balance of sodium, potassium, and water. BASIC PHYSIOLOGY Osmoregulation versus volume regulation One of the more confusing concepts in nephrology is the distinction between regulation of osmolality and regulation of extracellular volume (Table 22.1). Several factors contribute to this confusion. Concentration versus total quantity of sodium The first factor is the critical, though distinct, role that sodium plays in the regulation of osmolality vs the regulation of extracellular volume.

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