It is all about the response of organisms to its environment with reference to maintenance of osmoregulation and osmoconformation. It is useful for the PG students and teachers who teach animal physiology at the Masters level.

1. WATER AND OSMOTIC REGULATION
Dr. Nagabhushan CM
Assistant Professor,
Dept. Of Studies in Zoology,
Vijayanagara SriKrishnadevaraya University, Ballari,
Karnataka 583 104
nagabhushancm@vskub.ac.in
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2. What ?
• ORGANISMS are the aqueous solutions contained within
a membrane… ?
• Both the volume of the organism and the concentration of
solutes should be maintained within narrow limits,
• For optimal functioning animal requires TO MAINTAIN its
body fluids with a relatively constant composition.
• The problems of keeping water and solute concentrations
constant vary with the environment.
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3. terms
• Euryhaline organisms
• Stenohaline organisms
• Isosmotic organisms (Most marine invertebrates have
body fluids with the same
osmotic pressure as the sea water)
• Hyperosmotic
• Hyposmotic
• Osmo-Conformers
• Osmo-regulators
• The concentration of dissolved substances is expressed
in molarity (moles per liter solution) ex. A sol of 0.5
moles per liter is equal to 500 mmol per liter (millimole).
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4. • The osmotic concentration of a solution can be expressed
as the osmolarity (osmoles per liter).
• The osmolarity of a solution of a nonelectrolyte (e.g.,
sucrose or urea) equals its molar concentration.
• The osmolarity of an electrolyte (e.g., sodium chloride,
which in solution dissociates into Na+ and CI -- ) has a
higher osmotic concentration than is expressed by its
molarity.
• Isotonic v/s isosmotic are different (ex: blood in saline
and urea solution).
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5. osmoconformers
• As a rule
marine invertebrates are osmo-conformers, this does not
mean that their body fluids have the same solute
composition as sea water.
On the contrary, there are characteristic differences that
the animals must maintain, and this requires extensive
regulation of ionic concentrations.
• Must have a mechanism for eliminating some ions while
maintaining others at a higher level than that in the water.
Ex.the kidney.
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6. • Dialysis (Donnan’s effect of proteins) where salts and
ions can pass through the cellophane whereas the
proteins cannot.
• Echinoderms show no significant regulation of any ions.
• Aurelia regulates only SULPHATE by keeping its level
considerably below the sea water to maintain BUOYANCY
• Fast moving arthropods have LOW LEVELS OF Mg
whereas slow moving arthropods have HIGH LEVELS.
(Mg can act as an anaesthetic)
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7. Intracellular conc and vol regulation
• The concentrations of ions inside the cells are usually
very different from those outside;
• Ex. Sodium and chloride concentrations are
usually low inside the cells and high outside,
and potassium is usually high inside and low
outside.
• However, the cells are isosmotic with the surrounding
tissue fluid and blood, although the concentrations of
individual solutes differ.
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8. Thanks to aminoacids for constant cell volumes
• It is now well established that intracellular concentration
of free amino acids is an important factor in the control
of cell volume in salinity-stressed environments.
• As the salinity of water fluctuates, the amino acids in
the cells increase or decrease so that the cells remain
isotonic with the surroundings.
• DECREASE in AA concentration is achieved by the
synthesis of PROTEIN & INCREASE in AA is achieved
by the degradation of proteins.
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9. Animals in FW and BW
• Marine animals INTO brackish water === SURVIVE
• OSMOCONFORMERS  have same osmotic
concentration as the dilute medium
• OSMOREGULATORS  resist the dilution by
remaining hyper-osmotic.
• Marine animals INTO brackish water === SURVIVAL OF
PASSIVE OSMOCONFORMERS
OR
ACTIVE OSMOREGULATORS
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10. MECHANISM OF OSMOREGULATION
• When an animal is hyperosmotic to the surrounding medium,
it encounters two physiological problems:
• (1) water ENTERS into the animal (because of higher inside
concentration)
• (2) solutes tend to be LOST (because the inside
concentration is higher and because the water that enters
must be excreted and carries some solutes with it.)
• anal gills / gills / appendages maintain the
ion uptake by ACTIVE TRANSPORT is
evident by the increase in the OXYGEN UPTAKE.
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11. AQUATIC VERTEBRATES
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• The marine representatives fall into two distinct groups:
• 1. those whose osmotic concentrations are the same as or slightly
above sea water (hagfish, elasmobranchs, Latimeria, etc)
• 2. those whose osmotic concentrations are about one-third that of
sea water (lamprey, teleosts).
• The former group has no major problem of water balance, for if the
inside and outside concentrations are equal, there is no osmotic
water flow.
• In contrast, those who are hyposmotic live in constant danger of
losing water to the osmotically more concentrated medium.

12. cyclostomes
• Lampreys live both in the sea and in fresh water.
• have osmotic concentrations about one-quarter to one-third the
concentration of sea water.
• Hagfish are strictly marine and stenohaline.
• Hagfish are the only true vertebrates whose body fluids have salt
concentrations similar to that of sea water.
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13. elasmobranchs
• sharks and rays are almost without exception marine.
• They have solved the osmotic problem of life in the sea in
an interesting way.
• They maintain salt concentrations in their body fluids at
one-third the level in sea water, but they still maintain
osmotic equilibrium.
• This is achieved by adding to the body fluids large
amounts of organic compounds, primarily urea, &
TMAO so that the total osmotic concentration of their
blood equals or slightly exceeds that of sea water.
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14. teleosts
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15. The terrestrial environment
• The greatest physiological advantage of terrestrial life is
the easy access to oxygen;
• greatest physiological threat to life on land is the
danger of dehydration
• the rate of diffusion of water vapor into air increases
with increasing temperature and the diffusion rate
increases with decreasing barometric pressure
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16. Moist skinned animals
• Vapor – limited system (moist animals)
• Membrane-limited systems (insects with cuticle)
• Earthworms behaviour: hydro-permeable skin;
dehydrates and dies in dry soil / salty soil.
• Amphibians : live near the water/humid where evaporation
is LOW. Some aestivate in burrows &
restore water during rainfall.
• Snails: shell as barrier prevents evaporation.
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17. arthropods
• Bury during DAY AND COME OUT DURING NIGHT
• CRABS take up water from damp soil / substratum
• Woodlice live in moist decaying plant material.
• WAXY layer on the CUTICLE reduces evaporation.
• WATER BALANCE:
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WATER LOSS BY WATER GAIN BY
EVAPORATION FROM
BODY SURFACE,
DRINKING
RESPIRATORY ORGANS UPTAKE OF WATER BY
BODY SURFACE
FAECES UPTAKE OF WATER
FROM MOIST AIR
URINE WATER IN FOOD
OTHERS METABOLIC WATER

18. TERRESTRIAL VERTEBRATES
• 4 ORDERS of REPTILES
• Crocodiles  associated with water
• Snakes
• Lizards well adapted to DRY habitats.
• Tortoises
• There is close correlation betw evaporation and habitat.
• The drier the normal habitat, the lower the rate of
evaporation.
• In addition to water lost through evaporation, water is needed for
URINE FORMATION (therefore uric acid is excreted).
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19. TERRESTRIAL VERTEBRATES
• BIRDS AND MAMMALS
• Perspiration
• Panting
• Conservation of water/ using water from the metabolic
oxidation/ economic use of water in urine/ reduction in
respiratory evaporation.
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20. MARINE air-breathing vertebrates
• The excretion of excess salt, which the kidney is unable to
handle, is carried out by glands in the head called salt-
excreting glands or simply salt glands.
• The salt glands produce a highly concentrated fluid that
contains primarily sodium and chloride in concentrations
substantially higher than in sea water.
• The glands do not function continually, as the kidney
does; they secrete only intermittently in response to a salt
load
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21. Man in wild ocean
• Sea water is toxic to man and that a castaway at sea only
hastens the dehydration processes if he drinks sea water.
• The effect of drinking sea water on the water balance of a
man and of a whale:
1. A whale can drink 1 liter of sea water and
have a net gain of about one-third liter of pure water after
the salts are excreted.
2.The kidney of man is less powerful; the
maximum urine concentration is below that of sea water,
and if he drinks 1 liter of sea water, he inevitably ends up
with a net water loss of about one-third liter and is worse
off than if he had not drunk at al.
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22. Thus the organs of excretion are so
important for the maintenance of the
relative constant / steady state of internal
concentration and water content of
living organisms..
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