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Ch. 44 notes - Ch. 21:51 Two terms Osmoregulation process...

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Ch. 44 Osmoregulation and excretion 21:51 Two terms Osmoregulation – process by which animals control solute concentrations and balance water gain and loss Excretion – process that rids the body of nitrogenous metabolites and other metabolic waste products (which release ammonia, a toxic compound) Osmoregulation balances the uptake and loss of water and solutes Osmosis and osmolarity Osmosis occurs whenever two solutions separated by the membrane differ in osmotic pressure, or osmolarity (total solute concentration expressed in mol/L) mOsm/L human blood: 300 mOsm/L seawater: 1000 mOsm/L = 1 M isoosmotic – if 2 solutions separated by a selectively permeable membrane have same osmolarity hyperosmotic – solution with the greater concentration of solutes hypoosmotic – more dilute solution Osmotic challenges Osmoconformer – isoosmotic with its surrounsings Marine animals – most osmoconformers live in water that has a stable composition and hence have a constant internal osmolarity Osmoregulator – control internal osmolarity independent of that of its environment Lets animals live in environments uninhabitable for osmoconformers (freshwater/terrestrial habitats) Hypoosmotic: must discharge excess water Hyperosmotic: must take in water to offset osmotic loss Lets marine animals maintains internal osmolarity different from that of seawter
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Stenohaline – “narrow,” “salt,” cannot tolerate substantial changes in external osmolarity Euryhaline – “broad,” can survive large fluctuations in external osmolarity Euryhaline osmoconformers: Barnacles, mussels Euryhaline osmoregulators: striped bass, salmon Marine animals Marine invertebrates: mostly osmoconformers (osmolarity same as that of seawater) – no challenges in water balance, but have smaller concentrations of specific solutes than seawater must actively transport these solutes to maintain homeostasis Marine vertebrates + some marine invertebrates: osmoregulators – ocean = strongly dehydrating environonment Drink LOTS of seawater and use gills/kidneys to get rid of salts Gills: Chloride cells actively transport Cl - Na + follows passively Kidneys: excess calcium, magnesium, and sulfate ions are excreted with small loss of water Sharks (other chondrichthyans – cartilaginous animals) – like “bony fishes,” have an internal salt concentration much lower than that of seawater salt diffuses into their bodies, especially across gills. Unlike bony fishes, they are not hypoosmotic to seawater – shark tissue contains high concentrations of urea, a nitrogenous waste product of protein and nucleic acid metabolism. Shark’s body fluids also contain trimethylamine oxide (TMAO) – an organic molecule that protects proteins from damage by urea Salts + urea + TMAO = osmolarity close to seawater, but actually somewhat higher than 1,000 mOsm/L Water slowly enters shark’s body by osmosis and in food disposed of in urine from kidneys/lost in feces/secreted from a specialized gland Freshwater animals
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