Osmotic and Ionic Regulation

All animals face osmotic and ionic stresses.

Stresses depend on environment:• Aquatic

• Marine• Freshwater• Brackish (estuarine)

• Terrestrial

Regardless of their environment,all animals must be capable of

maintaining isosmoticity betweenthe ICF (intracellular fluid) and

ECF (extracellular fluid).

Regulating ICF osmotic conc. in responseto changes in the osmotic conc. of the ECF

is called:

Cell Volume Regulation

HYPERTONIC HYPOTONIC

Unchecked swelling under hypotonicconditions can lead to

OSMOTIC LYSIS

If the osmotic conc. of the ECF decreases,water moves into the ICF and the cell swells.

H2O

RegulatoryVolume

Decrease(RVD)

If the osmotic conc. of the ECF increases,water moves out of the ICF and the cell shrinks.

H2O

RegulatoryVolumeIncrease

(RVI)

RVI - Ionic Fluxes

osmoticallyshrunken

cell

Na+

H+

Cl-

HCO3-

H2O + CO2

H2O

H+

K+

Cl-

HCO3-

H2O + CO2

H2Oosmoticallyswollen

cell

RVD - Ionic Fluxes

ICFcontent

FWSW

H2O

F.A.A.

F.A.A. = free amino acids

FW SW

ICFcontent

Days0 15

H2O

F.A.A.

Animals can reduce the amountof volume regulation their cells

must do by regulating ECF osmoticconcentrations.

Osmotic and ionic regulation occursin both aquatic and terrestrial spp.

We’ll look at aquatic organisms first

Medium osmolarity (mOsm)

0 1000

1000

EC

F o

smol

arity

(m

Osm

)

isosmoticline

osmoconformer

osmoregulator

Stenohaline - able to tolerate a narrow salinity rangeEuryhaline - able to tolerate a wide salinity range

Volume changes on transfer to dilute seawater