Role of Water in Cellular Tissues - Essay Example

Role of Water in Cellular Tissues and the Connective Tissues Introduction Water is the predominant constituent of majority of the tissues in any living form. In animals it comprises 60% of the body weight, with 2/3rd in the intracellular and 1/3rd in the extracellular compartments (www.merckvetmanual.com). Of the extracellular water, 75% is in the interstitial tissue and the rest is in the intravascular region. Most of the animal cells are bound by the plasma membranes which are permeable to water and the total water content is maintained in a state of homeostatic equilibrium by the forces of osmotic pressure. Any change in the total water content of the body results in the maintenance of even distribution in all body compartments. However, when an isotonic solution is infused, only 1/4th of the volume infused remains in the intravascular space after some time due to the influence of osmotic and hydrostatic forces. The intravascular compartment contains molecules with large molecular weight which are incapable of crossing the semi permeable plasma membrane due to small size of the pores (www.merckvetmanual.com). These large molecules or colloids exert a force on the membrane due to the difference in osmotic gradient known as the colloidal oncotic pressure (COP). The difference in the COP and the hydrostatic pressure is responsible for the control of the fluid content in the intravascular space and the interstitial compartments. When intravascular hydrostatic pressure rises above the COP, fluid movement occurs in the direction of interstitial space resulting in rehydration or oedema depending on the pre-existing hydration status. Any increase in membrane pore size or high interstitial COP can also contribute to this phenomenon. The evolution of animal life has produced diverse life forms of various Phyla which have habitats as diverse as the depths of oceans to deserts and mountains. This has lead to the development of exclusive water regulatory mechanisms in different species. The mammalian water regulatory mechanisms are more or less uniform in structure, functioning and adaptive mechanisms. Terrestrial life involves the risks of desiccation as well as salt deficiency, which have important roles to play in water regulation of the body (Denton et al, 1996). The hypothalamus in the mid brain and kidneys are the important organs in mammalian species which play vital role in water regulation. In higher vertebrates, the hypothalamus is responsible for triggering and controlling mechanisms in response to external as well as internal disturbances to maintain the body homeostasis internally. The hypothalamic processes range from controlling behavioural patterns associated with ingestion of appropriate ingredients as a result of deficit, and control of the excretory processes during times of excess (Denton et al, 1996). All Metazoan organisms have developed a closed circulatory system and evolved organs that regulate and keep the ionic pattern constant regardless of change in the external environment. Renal regulation of body fluids and ionic composition is an important mechanism which aids in achieving the constant internal environment of the mammalian species. Deficiency of water during droughts, changes in ionic composition in diseases and other metabolic disorders are responsible for triggering appropriate homeostatic mechanisms. Any fluid deficit in the intravascular space results in reduced perfusion of the tissues and the resultant loss of tissue oxygenation. As the vascular wall tension decreases, there is a resultant stimulation of baroreceptors which results in a compensatory response. Intravascular water deficit is usually accompanied by concurrent extravascular deficit which results in dehydration. If the deficit persists and the compensatory mechanisms are unable to balance the ionic and water imbalance, the situation can be life threatening. Modern medicine usually balances the situation by the administration of appropriate fluids with physiologically apt solutions of the right constitution. Water as a molecule is one of the most amazing chemical entities in nature which is absolutely essential for the sustenance of life. Chemically it possesses a dissipative property and can dissociate into protons and electrons involved in pH and redox reactions and can react with a number of substances in nature (Ripl W., 2003). The molecular properties of water are such that their dynamics at various interfaces between liquid-liquid, solid-liquid and liquid-gaseous phase boundaries allow it play a central role in the genesis of life itself. It is a polar agent and is the most abundant solvent available in nature for the dissolution of salts as well as organic compounds. As far as the connective tissue integrity and the role played by water is concerned, it has been observed that osmotic retention of water within the matrix of the connective tissue is a major contributor of maintenance of its mechanical properties (Wells J.D., 1973). The net internal osmotic pressure inside a cartilage is has an important role to play in imparting capacity to resist pressure when it is subjected to load. The osmotic properties of connective tissue are attributed to the matrix of long chain mucopolysaccharides trapped within a fine collagen meshwork (Wells J.D., 1973). Man as well as domesticated animals are subject to close observation and have easy access to water sources. Wild animals however, are conditioned differently and the regulatory mechanisms involved in water as well other homeostatic functions offer an interesting field of study. Environmental physiology and responses to environmental variables are of prime importance in wild animals (Schmidt-Nielsen K., 1977). Responses of wild animals to environmental stress include temperature regulation and metabolic responses to extreme temperatures, use of water for temperature regulation, salt excretion and osmoregulation. In aquatic environments, lower aquatic vertebrates like fresh water fish and amphibians maintain a hypertonic environment within their bodies because they live in a dilute medium. Marine fish on the contrary maintain a hypotonic environment. The constitution of body fluids is naturally adjusted for survival in these extreme environs. Other animals that have partial habitat in water and completely terrestrial animals have adaptive osmoregulatory and excretory mechanisms which are directed towards preservation of water with the right amount of ionic components for the sustenance of life. Conclusion Water is the one of the most wonderful molecules of nature which is essential for sustenance of life, probably because the origin of life itself is believed to be from the oceans. The composition of body fluids including haemolymph and blood is remarkably similar to sea water. Adaptations in various life forms including microorganisms, plants and higher animals have taken place which supports the ideal composition of water content along with its soluble constituents inside the body, for the sustenance of life. References: Denton D.A., McKinley MJ. & Weisinger R.S., (1996), Hypothalamic integration of body fluid regulation, Proc. Natl. Acad. Sci. USA, Vol. 93, pp. 7397-740 Fluid Compartment Deficits, Online article available at: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/160403.htm Fluid Compartment Dynamics, Online article available at: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/160402.htm&word=water Ripl Wilhelm, (2003), Water: the bloodstream of the biosphere, Philosophical Transactions: Biological Sciences, Vol. 358, No. 1440, Freshwater and Welfare Fragility: Syndromes, Vulnerabilities and Challenges, pp. 1921-1934 Scmidt-Nielsen K., (1977), The physiology of wild animals, Proc. R. Soc. Lond. B. 199, 345-360 Wells J.D., (1973), Salt Activity and Osmotic Pressure in Connective Tissue. I. A Study of Solutions of Dextran Sulphate as a Model System, Proc. R. Soc. Lond. B. 183, 399-419 Read More