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Lecture 16

Lecture 16 BIOB34.doc

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University of Toronto St. George
Human Biology

Lecture 16 BIOB34 The last part of the course: Osmoregulation Key thoughts: Osmoregulation in different environments Control of ion and water balance: • Osmoregulation • Ionic regulation • Excretion of nitrogenous wastes Animals and their environments: - Environment has several different meanings: 1. External world for the whole animal 2. Extracellular fluid for a cell ( own fluid and own cell) ( REGULAT ION TRANSPORT) 3. Cytoplasm for intracellular enzymes ( RELATIVE TO EVERYTHING) - Animals use different combinations of tissues to control ion balance in various internal and external environments. ( conformers and regulators) ( outer protective layers, and exchange organs) Water balance and Concentration: - Internal Environment= aqueous solution • Volume and composition must be maintained within narrow limits ( ions and proteins in fluids and have to stay in a narrow minute) - Composition different from external environment • Composition tends to change towards eqm with the environment - Organism must control changes in composition of body fluids • Overall solute concentration ( Osmotic concentration) ( concentration of solute in the cells) • Concentration of specific solutes ( non salt related) Major types of hydric environments: DEPENDS ON TYPE OF ANIMALS Aquatic animals- high water availability: • Marine ( High solute concentration) ( Salt animals, sodium chloride) • Fresh water ( Low solute concentration)( LAKES AND PONDS) Terrestrial: Low water availability •Prevent water loss and maximize efficient osmo regulation because they are at a risk because the type of water they live in Ionic and osmotic Challenges: • Marine animals where animal tend to gain salts and lose water • Fresh water animals tend to lose salts and gain water • Terrestrial animals tend to lose water MOST ANIMALS MOVE BETWEEN ENVIRONMENTS AND MUST BE ABLE TO ALTER THEIR HOMEOSTATIC MECHANISMS!! 1) Marine invertebrates: - Typically osmoconformers: SHRIMP: concentration that is around them elevates the osmotic concentration to near these levels. Body fluids are isosmotic to sea water. THEY ARE HYPER OSMOTIC. Tend to have low relative osmotic concentration by hyper osmotic 2) Marine Vertebrates: SHARKS: ionic regulators, salt concentration 1/3 of sea salt and osmotic concentration because of the presence of organic solutes like urea - The salt levels are maintained at low levels: 1. Kidney: remove many ions, regulate ions and concentration 2. Rectal glad excretes fluid with high NACL concentration , remove high salt 3. Potential active excretion by gills, not fully known but there is some - Body fluids are slightly hyper osmotic: strict ionic regulators, can still regulate ions 1. Tends to draw water into the body 2. Water used in urine formation and rectal glad secretion 3) Fresh water invertebrates: Lobsters: - Typically osmoregulaters - Maintain hyper osmotic body fluid - Water tends to flow into the animal and they have osmotic uptake and ions tend to leave the body - HAVE DIFFUSION AND EXECRETION 4) Fresh water teleosts: - Hyperosmotic blood: water enters through the gills - Excrete dilute urine: Lose lots of solutes ( High volume) - Ions tend to be lost from the gills : Ions taken up in the food, active uptake of ions into the gills The role of epithelial tissues: - These tissues form boundary between animal and environment: External surfaces like skin and gills. Internalized surfaces like human digestive systems and excretory systems - These tissues have physiological functions in respiration, digestion and ion wand water regulation - Protective coatings - Not just serve the purpose for ion exchange, for digestion and respiration and what not. THEY HELP FOR GAS EXCHANGE and what not Terrestrial organisms: Easy access to oxygen Bad: Danger of dehydration Overtime, water gain must equal water loss Ways of losing water: - Evaporation: Body surface and respiratory surface - Execration/secretion: Feces, urine, other secretions Ways of gaining water: - Drinking eating; Water in food, drinking water and juice - Integumental uptake: From water, from air ( In amphibians because they stay in water and in land) - Metabolic water Approaches for terrestrial animal: it’s not all perfect and rosy, they still have disadvantages Vapor limited system: - Permeable integuments - Rate of water loss determine by transfer of water to surrounding air Membrane limited system: - Surface provides resistance to evaporation - Rate of evaporation altered by changing membrane permeability - Evaporation doesn’t occur so easily The integument is an osmotic barrier: - Animals change flux of water across the body surface by mediating permeability of the integument  Aquaporin proteins increase water permeability 100-fold - Typically animals need to reduce water flux:  Cover external surfaces with layer of hydrophobic molecules 1) Mucus ( Like snails) 2) Stratum corneum with keratin ( Terrestrial amniotes) 3) Cuticle w
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