Water Balance

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Water Balance

• Comparative Animal Physiology

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Today
I. Terminology units II. Water balance
challenges of different environments III.
Osmoregulatory abilities in water IV. Water
conservation by terrestrials V. Animal of the Day
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Terms
1.Osmolarity v. molarity- 1 M NaCl 2 Osm
solution 2. Isosmotic v. hypo/hyperosmotic tonici
ty relates to cells permeability 3. CONFORMER
v. REGULATORS 4. Stenohaline (narrow)
Euryhaline (tolerant)
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Marine environment- verts
CONFORMERS Hagfish /Sharks/Rays -isosmotic (1
Osm) Water loss? regulate kinds of
osmolytes use urea NaCl diffuses in, out via
kidney REGULATORS Bony fish- hypoosmotic drink
seawater active xport NaCl out via gills
excrete Ca, Mg SO4 via urine Tetrapods-
hypoosmotic from food or from drinking seawater
(birds reptiles)
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Solutes in marine fish
Ionic solutes replaced by organic solutes
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Protein membrane transporters
Active transport- against concentration
gradient Na/K ATPase- 3Na/2K electrogenic Antiport
er- exchange using one concentration gradient
against another Symporter- 2 substances in same
direction driven by one concentration
gradient Aquaporin- water channel in lipid bilayer
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Marine environment- inverts
CONFORMERS Cellular osmotic tolerance-
intracellular amino acid osmolytes increase
(Why?) Organic solutes less problem w/ proteins
than ions.
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Freshwater environment
Hypoosmotic (5-50 mOsm) so lose solutes gain
H2O 1. Active transport salts into body. 2.
Excrete large amounts H2O but retain salts via
kidney (active xport again) Na pump in fish
gills, frog skin, turtle bladder, mamm kidney /
tight junctions
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Brackish waters
Often euryhaline. Few regulate hypoosmotic
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Terrestrial environment
Water loss is critical, but must excrete
organic wastes (urea etc). INPUTS 1. Drink/eat
(cheating) 2. Metabolism- oxidation of food makes
H2O e.g. camel humps 3. Air- use salt to
absorb (ticks, mites, apterygotes) OUTPUT 1.
Evaporative water loss. 2. Expect concentrated
urine/feces to retain H2O
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Three ways to gain water
Lizard
Source of water inputs ()
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Two ways to lose water
Less permeable skin.
Note Total evaporative water loss in mg/g/hr
is indicated for each organism.
Total evaporative water loss ()
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Temporal counter-current
Warm-lunged animals hydrate air as it enters to
keep lungs moist to facilitate gas
exchange. Exhalation would lose that water. Resp
surfaces absorb heat w/ blood counter-current.
(Why use counter-current in blood
vessels?) After inhalation, (temporary)
temperature gradient set. More effective when air
cooler than inside animal. Narrower is better.
Why?
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Temporal counter-current
Stronger gradient
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THE ANIMAL OF THE DAY (PhChordata, GeRhiniodon)
The whale shark, isosmotic with sea water Retain
urea--the major metabolic by product of protein
deamination--to make up the difference in
osmolarity between their ionic content and the
osmolarity of sea water. In addition their blood
contains a large amount of trimethylamine oxide
(TMAO), which counteracts the toxic effects a
high urea concentration usually exerts on enzymes
(denaturation).
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Amphibians water loss