Biology 2672a: Comparative Animal Physiology Why is blood red (or green, or blue)?
Biology 2672a: Comparative Animal Physiology Osmoregulation in fishes.
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Transcript of Biology 2672a: Comparative Animal Physiology Osmoregulation in fishes.
Biology 2672a: Comparative Animal
Physiology
Osmoregulation in fishes
Freshwater fish
Inside:
300 mOsm
High Na+ & Cl-
Outside:
<5 mOsm
Low Na+ & Cl-
Water
Salts
Saltwater fish
Inside:
300 mOsm
Low Na+ & Cl-
Outside:
1000 mOsm
High Na+ & Cl-
Salts
Water
Terrestrial fish
Inside:
Wet
High Na+ & Cl-
Outside:
Dry
No Na+ & Cl-
SaltsWater
OsmoregulationMaintenance of water and salt
balance in the bodyWhy freshwater fishes don’t
explode, saltwater fishes don’t dry up and people don’t desiccate
Osmolarity/OsmolalityThe amount of ‘stuff’ in a
solution1 Mole of solutes = 1 OsmoleCumulative: 0.2 M of 5 things = 1
OsmoleOsmolality – per kg of solventOsmolarity – per litre of solvent
Osmotic pressureSolutes exert pressure that
moves water from place to placeCan be a source of hydrostatic
pressure…
OsmosisMovement of water across a
semi-permeable membrane
Net movement of water driven by osmotic pressure
Osmosis and hydrostatic pressure
Osmotic pressure has caused bulging – hydrostatic pressure
Osmoconformers and Osmoregulators
External Osmolarity(mOsm)
Inte
rnal O
sm
ola
rity
(mO
sm
)
Fig. 26.3a,b
Many different types and combos of osmoregulatory strategies
Fig. 26.3c
Strategy and Tolerance are not identical
External Osmolarity
Inte
rnal
Osm
ola
rity Osmoregulator
Osmoconformer
Euryhaline
Stenohaline
External Osmolarity
Inte
rnal O
sm
ola
rity
Inte
rnal [N
a+
]In
tern
al [U
rea]
Inside OutsideNa+ 286 mMCl- 246 mMOthers 135 mM
667 mOsm
Na+ 286 mMCl- 246 mMUrea 351 mMOthers 135 mM
1018 mOsm93
0 m
Osm
From Table 26.5
Ureo-osmoconformer
External Osmolarity
Inte
rnal O
sm
ola
rity
Inte
rnal [N
a+
]In
tern
al [U
rea]
But Urea is Bad!Chaotropic
Binds strongly to proteins, releasing water and disrupts tertiary structure
Km
Concentration
Urea
Effects of solute concentration on enzyme function
Trimethylamine oxide(TMAO)
N+
CH3
H3C CH3
O-
Counteracting Solutes
Fig 26.10
Inside Outside
Na+ 286 mMCl- 246 mMUrea 351 mMTMAO 71 mMOthers 64 mM
1018 mOsm
930
mOsm
From Table 26.5
Ureo-Osmoconformation in sharks Urea is used to make up the ‘osmotic
gap’ between internal and external concentration Requires high protein diet for
manufacturing Urea TMAO acts as a counteracting solute
to preserve protein function in high concentrations of urea.
Why would you soak shark prior to cooking it?
The situation for a marine teleost
Fig 27.7b
Gills as exchange organsCO2 & O2
Used to remove the salts that are ingested with food and water (and absorbed through gill
surfaces) Major site for this in marine
teleosts
How many ions? Total daily flux estimated for
intertidal Xiphister atropurpureus in seawater ~10-40 g
Na+: 110 mM/kg fish/day 0.25g for a 10 g fish (2.5% bw)
Cl-: 72 mM / kg fish/day 0.25 g
Water: 2480 ml/kg fish/day 24.8 g water for a 10 g fish (!)
Evans (1967) J. Exp. Biol. 47: 525-534
Chloride cellsWater
Blood
Apical(Mucosa)
Baso-lateral(serosa)
Pavement cell
Fig. 27.6
Export of Chloride
Box 27.2
Export of Chloride is driven by a Na+ gradient
Box 27.2
Active removal of Cl- leads to an electrochemical imbalance that drives Na+ out of blood via paracellular channels
Box 27.2
Chloride cell summaryTranscellular transport of Cl-
Driven by Na+,K+-ATPase (requires energy)
Paracellular transport of Na+
Ionoregulation accounts for ~3-5% of resting MR in marine teleosts
The situation for a freshwater teleost
Fig. 27.7a
Gills as exchange organsCO2 & O2
Used to take up salts from the environment Not much NaCl in freshwater, but
gills process a huge volume
Chloride cells again
Figs 27.3 & 27.4
Exchange of CO2 wastes for NaCl
Fig. 26.2
Na+ uptake
Box 4.1 Fig.A(2)Note tight junction
Cl- uptake
NaCl uptake summaryExchange for CO2
Na+ via electrochemical gradient Cl- via HCO3
- antiport
Very dilute urine gets rid of excess water without losing too much salt
Salt Water Fresh Water
Drinking Lots Little
Urine Little, concentrated Copious, dilute
Ion flux Passive into fish; active out of fish
Na+,K+-ATPase Na+ into bloodstream
Tight junctions Yes
Cl- Transcellular transport driven by Na+ gradient
Transcellular via HCO3- antiporter (driven by H+ pump)
Na+ Paracellular driven by electochemical gradient
Transcellular driven by electrochemical gradient (set up by H+ pump and Na+,K+-ATPase)
Reading for ThursdayWater balance in
terrestrial organisms
pp 700-712