Lecture 18 and 19 Water and electrolyte balance Chapter 40.pdf

Lecture 18 and 19 Water and electrolyte balance Chapter 40.pdf

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Introductory Biology II ABIO 131 Professor Elise Gervais, PhD Lecture 18 and 19 Chapter 40 Water and Electrolyte Balance
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Osmoregulation Electrolytes and water move through organisms by: Diffusion - the movement of uncharged substances down their concentration gradients Osmosis - the movement of water down its concentration gradient across a semipermeable membrane A solution’s osmolarity is the concentration of solutes in a solution measured in osmoles per liter Osmoregulation is the process by which organisms control the concentration of water and solutes within their bodies
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Osmolarity Solutes and water move from areas of high to low concentration
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Osmotic Stress in Marine Fish Osmoregulation is required in marine vertebrates because seawater is hyperosmotic to their tissues Water tends to flow by osmosis out of the gill epithelium so marine fishes must replace the water or the cells will shrivel and die Marine fishes must drink large amounts of water to replace the loss of water, which also brings more electrolytes when ions diffuse into the gill epithelium down their concentration gradient To rid themselves of these excess electrolytes, marine bony fishes actively pump ions out into the seawater by excreting small quantities of highly concentrated urine
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Osmotic Stress in Freshwater Freshwater animals are under osmotic stress because they gain water and lose solutes The freshwater is hyposmotic to the fishes’ tissues - The gain of water across the gill epithelium puts them under osmotic stress If a freshwater fish does not get rid of incoming water, its cells will burst and it will die To achieve homeostasis, they excrete large amounts of water in their urine and don’t drink Electrolytes diffuse out of the gill epithelium into the environment The fishes replace electrolytes by eating food or actively transporting them into the body
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Salmon Model Systems Over the course of a lifetime, sea bass and several salmon species move between salt water and freshwater Thus they move between environments with dramatically different osmotic stresses The gill epithelia of marine fishes have specialized cells called chloride cells, which are capable of moving salt using membrane proteins When sea bass and salmon are in salt water, these cells are abundant and active
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Osmotic Stress on Land
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