topic23 - BIOL 1030 TOPIC 23 LECTURE NOTES Topic 23...

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BIOL 1030 – TOPIC 23 LECTURE NOTES Topic 23: Excretory System (Ch. 44) I. functions A. osmoregulation : maintaining the correct level of water and ions in the body 1. osmotic pressure : tendency of a solution to take in water by osmosis 2. osmolality : total moles of solute per kilogram of water (measure of solute concentration, directly related to osmotic pressure) 3. isotonic : same solute concentration as surroundings (osmotic pressures in balance; no net movement of water) 4. hypotonic : lower solute concentration than surroundings (outside has more osmotic pressure; water moves out by osmosis) 5. hypertonic : higher solute concentration than surroundings (solution has more osmotic pressure; water moves in by osmosis) 6. osmoconformers : in osmotic equilibrium (isotonic) with their environments – some sea animals, including sharks; little or no need for active osmoregulation 7. osmoregulators : actively maintain a specific osmotic pressure, usually in an osmotic imbalance with their environment; in vertebrates: hypotonic relative to environment: most marine vertebrates (osmolality about 1/3 of seawater); must keep from losing too much water; terrestrial vertebrates – constantly lose water by evaporation, must keep from losing too much hypertonic relative to environment: freshwater fish, amphibians in water and most moist terrestrial areas; constantly taking in water, must get rid of excess water B. selective retention: sorting what solutes are excreted vs. retained (gets rid of wastes, keeps what the body needs) II. structures (vertebrate kidney – focus on mammalian kidney) A. kidneys : pair of bean-shaped organs; perform most functions of the excretory system 1. renal cortex – outer portion of kidney 2. renal medulla – inner region of kidney 3.
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