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Biological Sciences
Course Code
Mary Olaveson

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How do vertebrates maintain salt and water balance?
oMajor excretory organism is the kidney for vertebrates
oWithin the kidney the actual functional unit is called the nephron
Marine Animals- Bony Fishes
oMost marine invertebrates are osmoconformers: bodily fluids are adjusted or
react and to similar conditions animals find theirselves in the environments
oMost marine vertebrates/some invertebrates are osmoregulators: actively
adjusting their solute situations to deal with water issues and therefore
maybe maintaining conditions within their cells and bodily fluids that are
different than their external environments
oMarine bony fishes: bodily fluids and intracellular conditions are hypoosmotic
to sea water: more water, more dilute...issue of losing water from tissues to
outside environment and they can become dehydrated
oSolution: taking in water when feeding and salts from marine water. So they
need to try to retain their water and get rid of excess salts...they can get rid of
salts across their gills and can adjust water loss across their gills and across
other parts of their body surfaces because those are parts that are going to
lose water to the external environment
oFew glomeruli: less blood being brought to the kidneys for exchange and urin
tends to be more concentrated than that of fresh water fish because they’re
trying to hold the water not lose it to the external environment
oNitrogenous waste (ammonia) can be get rid of through gills as well
Freshwater Animals- Bony Fishes
oTheir bodily fluids and internal cellular conditions are more concentrated
than their external environment so they’re hypo-osmotic to their environment
so consequently they’re going to be taking up water from a dilute external
oThey’re taking up water and ions from their food, and salt through gills, and
taking in water across gills and other bodily surfaces because the water
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outside is more dilute than the internal conditions of the fish so water moves
into the fish
oProblem: have too much water
oThey have much more developed kidney and designed to get rid of water
oThey dont concentrate their urin they’re trying to get rid of water so urin is
oPart of life cycle in water and part on land
oCan breathe across skin (they have gas exchange) so its important that skin
is moist but they actually dont have much permeability across skin because
organisms dont want to be losing water across the skin surface and become
oEstivation: state of low metabolic activity/low water demand
oEctothermic so at low temperatures they wont be very active
oDuring estivation they can fill their bladder with a lot of water in the form of
dilute urin and hang onto that and when they go onto the resting period they
can reabsorb the water from t his bladder and not become dehydrated
oDehydration is an issue
oDeveloped reproduction method: produce eggs that have shelled eggs which
reduces permeability of water and reduces dehydration from the internal egg
conditions where the embryo is developing
oHave scaled skin that prevents water loss
oExcrete their ammonia/nitrogenous wastes as uric acid and in doing so they
have concentrated their urin/wastes so that theres very little water loss and
this can prevent dehydration
Birds and Mammals
oEndothermic =issues of maintaining internal body temperature so it impacts
how they deal with water/salt issues
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