Biology 272b: Comparative Animal Physiology

Biology 272b: Comparative Animal Physiology

Biology 2672a: Comparative Animal Physiology Osmoregulation in fishes Freshwater fish Water Inside: Outside: 300 mOsm

<5 mOsm High Na+ & Cl- Low Na+ & Cl- Salts Saltwater fish Salts Inside:

Outside: 300 mOsm 1000 mOsm Low Na+ & Cl- High Na+ & Cl- Water

Terrestrial fish Inside: Outside: Wet Dry High Na+ & Cl-

No Na+ & Cl- Salts Water Osmoregulation Maintenance of water and salt balance in the body Why freshwater fishes dont

explode, saltwater fishes dont dry up and people dont desiccate Osmolarity/Osmolality The amount of stuff in a solution 1 Mole of solutes = 1 Osmole Cumulative: 0.2 M of 5 things = 1 Osmole

Osmolality per kg of solvent Osmolarity per litre of solvent Osmotic pressure Solutes exert pressure that moves water from place to place Can be a source of hydrostatic pressure Osmosis

Movement 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

Internal Osmolarity (mOsm) Osmoconformers and Osmoregulators Fig. 26.3a,b External Osmolarity (mOsm)

Many different types and combos of osmoregulatory strategies Fig. 26.3c Strategy and Tolerance are not identical Euryhaline Internal Osmolarity

Stenohaline Osmoconformer Osmoregulator External Osmolarity External Osmolarity Internal [Na+] Internal [Urea] Internal Osmolarity

Inside Outside From Table 26.5 m 286 mM 246 mM 351 mM 135 mM

1018 mOsm 93 0 Na+ ClUrea Others O sm

Na+ 286 mM Cl246 mM Others 135 mM 667 mOsm Internal [Na+] Internal [Urea] Internal Osmolarity Ureo-osmoconformer

External Osmolarity But Urea is Bad! Chaotropic Binds strongly to proteins, releasing water and disrupts tertiary structure Effects of solute concentration

on enzyme function Km Urea Concentration Trimethylamine oxide (TMAO) CH3 H3C

N+ O- CH3 Counteracting Solutes Fig 26.10 From Table 26.5

O sm m Na+ 286 mM Cl246 mM Urea 351 mM TMAO 71 mM Others 64 mM

1018 mOsm Outside 93 0 Inside 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 organs CO2 & 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 Na+: 110 mM/kg fish/day

0.25g for a 10 g fish (2.5% bw) Cl-: 72 mM / kg fish/day ~10-40 g 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 cells Water Apical

(Mucosa) Pavement cell Blood Baso-lateral (serosa) 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 summary Transcellular transport of Cl- Driven by Na+,K+-ATPase (requires energy) Paracellular

transport of Na+ Ionoregulation accounts for ~35% of resting MR in marine teleosts The situation for a freshwater teleost Fig. 27.7a Gills as exchange organs CO2

& 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 Note tight junction Box 4.1 Fig.A(2)

Cl- uptake NaCl uptake summary Exchange 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 Thursday Water

balance in terrestrial organisms pp 700-712

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