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Osmotic and Ionic Regulation
All animals face osmotic and ionic stresses.
Stresses depend on environment:
• Aquatic
• Marine
• Freshwater
• Brackish (estuarine)
• Terrestrial
SW
inve
r
Elas t.
mob
ranc
h
Tele
ost
FW
inve
rt.
ICFConc.(mOsm)
BlodConc.(mOsm)
1
0
0
0
io
n
s
o
r
g
a
n
ic
s
5
0
0
0
1
0
0
0
io
n
s
o
r
g
a
n
ic
s
5
0
0
0
Regardless of their environment,
all animals must be capable of
maintaining isosmoticity between
the ICF (intracellular fluid) and
ECF (extracellular fluid).
Regulating ICF osmotic conc. in response
to changes in the osmotic conc. of the ECF
is called:
Cell Volume Regulation
HYPERTONIC
HYPOTONIC
Unchecked swelling under hypotonic
conditions can lead to
OSMOTIC LYSIS
If the osmotic conc. of the ECF decreases,
water moves into the ICF and the cell swells.
H2O
Regulatory
Volume
Decrease
(RVD)
If the osmotic conc. of the ECF increases,
water moves out of the ICF and the cell shrinks.
H2O
Regulatory
Volume
Increase
(RVI)
RVI - Ionic Fluxes
Na+
H+
H2O + CO2
ClHCO3osmotically
shrunken
cell
H2O
RVD - Ionic Fluxes
H+
K+
H2O + CO2
HCO3Cl-
osmotically
swollen
cell
H2O
F.A.A. = free amino acids
ICF
content
H2O
F.A.A.
SW
FW
F.A.A.
ICF
content
H2O
0
FW
SW
Days
15
Animals can reduce the amount
of volume regulation their cells
must do by regulating ECF osmotic
concentrations.
Osmotic and ionic regulation occurs
in both aquatic and terrestrial spp.
We’ll look at aquatic organisms first
ECF osmolarity (mOsm)
1000
isosmotic
line
osmoregulator
osmoconformer
1000
0
Medium osmolarity (mOsm)
Stenohaline - able to tolerate a narrow salinity range
Euryhaline - able to tolerate a wide salinity range
Volume changes on transfer to dilute seawater