containing waste products of metabolism. Controlling the Internal EnvironmentAquatic animals: Maintain water balance by compensating for net osmosis between external environment and internal fluids: Isosmotic external environment There is no net movement of water by osmosis. Hypo-osmotic external environment Water will move from the external environment to the internal fluids. Hyperosmotic external environment Water will move from the internal fluids to the external environment.Marine Animals: 1. Osmoconformers most marine invertebrates May still need to regulate internal concentrations of specific ions. Usually slight, but may be significant. 2. Osmoregulators most marine vertebrates a. Cartilaginous fish (eg, sharks) b. Bony fishMaintain a lower osmolarity for NaCl than seawater. NaCl diffuses through gills. Excrete NaCl: a. Kidneys (some) b. Rectal glands (salt excretory glands) Cartilaginous fishBody fluids still slightly hyperosmotic to seawater Due to accumulation of urea and trimethlyamine oxide (TMAO) in fluids. Water slowly enters body by osmosis. Kidneys eliminate excess water as urine.Body fluids are hypo-osmotic to seawater. Constant loss of water to surroundings by osmosis. Constant gain of salt by diffusion and in food. Bony marine fishes:Drinking large quantities of seawater and pump out excess salt through gills and skin. Chloride cells in gills pump chloride ions out, sodium follows passively. Kidneys excrete only small amounts of water.Body fluids are hyperosmotic to fresh water. Constantly taking water in by osmosis. Constantly losing salt by diffusion. Freshwater Animals: perchExcrete large volumes of dilute urine and regain lost salts. Chloride cells in gills pump chloride ions in, sodium follows passively. Ingest salt in food.Terrestrial animals: Covered by relatively impervious surfaces to prevent dehydration: Nervous and hormonal mechanisms to control thirst. Kidneys conserve water and concentrate urine.Nitrogenous Wastes: Metabolism of proteins and nucleic acid produces nitrogenous waste = ammonia Ammonia is eliminated as Ammonia very toxic – – – – – – – – – – – – – – – – – – – Continued [Show less]
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