Osmoregulation and Excretion

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They balance water loss by drinking seawater and excreting salts.

Slide 10

Osmoregulation in marine and freshwater bony fishes: a comparison: drinking, gills, urine …

Excretion

of salt ions

from gills

Gain of water and

salt ions from food

Osmotic water

loss through gills

and other parts

of body surface

Uptake of water and

some ions in food

Uptake

of salt ions

by gills

Osmotic water

gain through gills

and other parts

of body surface

Excretion of large

amounts of water in

dilute urine from kidneys

Excretion of salt ions and

small amounts of water in

scanty urine from kidneys

Gain of water

and salt ions from

drinking seawater

Osmoregulation in a saltwater fish

Osmoregulation in a freshwater fish

Slide 11

Freshwater Animals

Freshwater animals constantly take in water by osmosis from their hypoosmotic environment.

They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine.

Salts lost by diffusion are replaced in foods and by uptake across the gills.

Slide 12

Animals That Live in Temporary Waters

Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state.

This adaptation is called anhydrobiosis.

Slide 13

Anhydrobiosis - adaptation… Hydrated = active state dehydrated = dormant state.

(a) Hydrated tardigrade

(b) Dehydrated

tardigrade

100 µm

100 µm

Slide 14

Land Animals

Land animals manage water budgets by drinking and eating moist foods and using metabolic water.

Desert animals get major water savings from simple anatomical features and behaviors such as a nocturnal life style.

Slide 15

Water balance in two terrestrial mammals

Water

gain

(mL)

Water

loss

(mL)

Urine

(0.45)

Urine

(1,500)

Evaporation (1.46)

Evaporation (900)

Feces (0.09)

Feces (100)

Derived from

metabolism (1.8)

Derived from

metabolism (250)

Ingested

in food (750)

Ingested

in food (0.2)

Ingested

in liquid (1,500)

Water

balance in a

kangaroo rat

(2 mL/day)

Water

balance in

a human

(2,500 mL/day)

Slide 16

Energetics of Osmoregulation