Download osmoregulation

Osmoregulation
The solute and water content of the
internal environment must be regulated.
Known as osmoregulation.
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What is osmotic concentration?
• This is the total concentration of all the
osmotically active particles in a liquid
• Osmotically active particles include Sodium and
potassium. But basically any molecule of a
solute in solution can be ‘osmotically acitve’
• Eg: a solution of water with 5 molecules of
sodium chloride (NaCl) would have a 10
osmotically active particles. 5 sodium and 5
chlorines.
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Osmoregulation
Mechanisms for obtaining, retaining and
eliminating water and solutes vary
considerably depending on whether the
organism is marine, freshwater or
terrestrial.
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How can water be lost from an organism?
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Water loss
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By evaporation from skin/exoskeleton
In faeces and urine
From airways (exhalation of moist air
from respiratory surfaces)
Sweating
Panting
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Terrestrial animals
The primary water balance problem for
terrestrial animals is water loss.
Mechanisms to retard water loss:
• Behavioural adaptations
• Dry, scaly skin of reptiles
• Production of concentrated wastes
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Marine fish
Marine fish have body fluids that are more
dilute than the surrounding water and so
tend to lose water by osmosis.
To achieve water balance marine fish:
• Drink sea water (to balance salt levels and
reduce water loss)
• Produce small volumes of concentrated
urine (to reduce water loss)
• Actively excrete salts at the gills
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Freshwater fish
Water tends to enter tissues of freshwater fish
by osmosis and must be expelled to avoid
flooding the body.
To achieve water balance, freshwater fish:
• Rarely drink (they get heaps of water diffusing in
from outside)
• Produce large volumes of dilute urine (to get rid
of water)
• Actively take up salts at the gills (to maintain
stable osmotic concentration)
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Excretion of Nitrogenous Wastes
• Formed from protein breakdown in cells of
animals
• All amino acids contain nitrogen
• When broken down for energy the nitrogen is
split off and forms ammonia (NH3)
• Ammonia is toxic to cells and must be excreted
• Ammonia can then be converted into Urea or
Uric acid which are much less toxic to the cells
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• Ammonia: Highly toxic and needs a lot of
water to excrete. Generally used only by
aquatic animals
• Urea: Much less toxic but also requires a
fair bit of water to excrete and energy to
make. Used by mammals and
cartilaginous fishes
• Uric Acid: Large molecule with low toxicity.
Takes a lot of energy to make but requires
very little water to excrete. Used in reptiles
and birds.
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Osmoregulation in Humans
The hypothalamus is involved in
osmoregulation.
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What if there is not enough
water?
When the hypothalamus detects too little
water in the blood:
1. Sends message to pituitary gland to
release ADH.
2. Collecting duct becomes permeable to
water. Water moves by osmosis into
nearby capillaries.
3. Less water is lost in urine, urine is
concentrated.
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What if there is too much
water?
When the hypothalamus detects too
much water in the blood:
1. It stops signalling pituitary gland to make
ADH.
2. In the absence of the hormone, the
collecting duct becomes impermeable to
water, urine is dilute.
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The concentrating ability of desert rodents depends on a
thick renal medulla and long loops of henle
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