osmoticbalance-notes - BIOL 326 General Physiology Lecture...

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Page 1 of 4 BIOL 326 - General Physiology Lecture Notes : Osmoregulatory systems and The stress of dehydration in animals . March 8-10, 2010 Dr M. Sweeney-Nixon Objectives: At the end of this section, you will be able to describe in general terms how (and why) animals osmoregulate. Why balance water in cells ? A major requirement for cell survival is the retention of appropriate quantities of water within the cell (studied in cell physiology section): to maintain the concentration of ions and organic molecules in the cytosol & extracellular compartments, to maintain a specific shape and to prevent lysing. Thus, cells require a balance between water uptake and loss. Whether an animal lives in salt water, fresh water, or on land, water gain must balance water loss in its cells. Interstitial fluid must be in osmotic balance with the cytosol. Terrestrial and salt water animals face water losses, while animals in fresh water face salt losses (gain of water) - see below. Why balance water in organisms ? Much of the water in organisms is in the extracellular fluid, including blood and hemolymph. These fluids are mostly water (species specific; the fluid part of blood is called the plasma) as studied in the cardiovascular section. Loss of water from the plasma (dehydration) would increase the concentration of dissolved substances and would cause dehydration of cells and tissues as water osmoses out of the tissues into the blood. As well, loss of water from plasma (dehydration) decreases blood pressure, and this is a major stressor for an animal . Remember that blood pressure, defined as hydrostatic pressure exerted by blood against its vessels, is created by ventricular systole i.e. heart beating (hence systolic b.p.). Thus blood pressure is proportional to cardiac output (see CP notes). It is essential to pump blood from the heart (high pressure) to body parts (lower pressure) e.g. feeding the brain. It also is proportional to blood volume (which decreases in dehydration). What triggers dehydration (or increase water) in animals, thus requiring osmoregulation? Water in terrestrial animals is lost through breathing . Animals must feed and metabolize food in order to survive. This provides water and solutes through ingestion or metabolism [some reactions consume water (e.g. hydrolysis reactions)], and produces water soluble wastes (e.g.
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This note was uploaded on 03/30/2010 for the course BIOLOGY 326 taught by Professor James during the Spring '10 term at York University.

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osmoticbalance-notes - BIOL 326 General Physiology Lecture...

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