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‫االسراء اية ‪58‬‬
By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Member of American Society of Physiology
Test Yourself
• Na+ - K+ ATPase is inactivated by which of
the followings :
• a) high intracellular [ Na+ ] .
• b) high extra cellular [K+] .
• c) availability of ATP .
• d) cardiac glycosides .
• e) thyroxin hormone .
Biophysics , Abdelaziz Hussein
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Test Yourself
• Solute movement by active transport can be
distinguished from solute transport by
facilitated diffusion because active transport;
1. Is saturable at high solute concentration
2. Is inhibited by other molecules with structures
similar to that of the solute
3. Moves the solute against its electrochemical
gradient
4. Allows movement of polar molecules
Biophysics , Abdelaziz Hussein
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Test Yourself
• A sodium channel that opens in response to
change in membrane voltage is an example of
1. A ligand-gated ion channel
2. An ion pump
3. A voltage -gated ion channel
4. A peripheral membrane protein
Biophysics , Abdelaziz Hussein
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Test Yourself
• The Na-K pump is
1. A peripheral protein.
2. An integral protein.
3. A glycolipid.
4. A phospholipid.
Biophysics , Abdelaziz Hussein
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Biophysics , Abdelaziz Hussein
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Water Channels (Aquaporins)
Peter Agre
2003 Nobel Prize,
Chemistry
Water
Solute
9
It is the passive flow of water across a semipermeable (selectively permeable) membrane
down a concentration gradient of water i.e.
 From high concentration of water to low
concentration of water or
From low concentration of solute to high
concentration of solute
Biophysics , Abdelaziz Hussein
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Osmolarity
• It is the number of osmoles per one liter of
solution.
Osmolality
• It is the number of osmoles per one Kg of
solvent.
Biophysics , Abdelaziz Hussein
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At Cellular Level
Biophysics , Abdelaziz Hussein
At Capillary Level
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a) At the cellular level
The ECF and ICF are osmotically equal and any change
in plasma osmolarity causes cells to shrink or swell
Plasma osmolarity
•290 mosmol/L
ICF= 290
mosoml/L
ICF= 290
mosoml/L
ICF= 290
mosoml/L
Osmolarity = 290
mosoml/L
Biophysics , Abdelaziz Hussein
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Tonicity
•It is the ability of a solution to affect fluid volume
and pressure within a cell.
•It depends on concentration and permeability of
solute
•It is a property of a solution in reference to
particular membrane.
Biophysics , Abdelaziz Hussein
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•Solutions are 3 types according to its tonicity
Solution
Isotonic
Hypertonic
Hypotonic
solution
solution
solution
Biophysics , Abdelaziz Hussein
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a) Isotonic Solution
Isotonic solution has the
same osmolarity as
plasma and causes no
change in cell volume
e.g. NaCl solution 0.9 %
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b) Hypotonic Solution
•Hypotonic solution has
osmolarity less than the
plasma which causes
drawing water into the
cell resulting in cell
swelling
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c) Hypertonic Solution
•Hypertonic solution has
osmolarity higher than
the plasma which causes
drawing water out of the
cell resulting in cell
shrinkage
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 Hyperosmolarity can cause coma
 Hyposmolarity can cause convulsions
When the cell is exposed to hypotonic fluid it
will swell → activates channels in the cell
membrane → allow increased efflux of K, Cl and
organic anions, and small organic solute →
water follows these osmotically active particles
out of the cell → the cell resumes its original
volume.
Biophysics , Abdelaziz Hussein
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Any change in the cell volume due to change in
ECF osmolarity can be calculated from the
following equation;
Biophysics , Abdelaziz Hussein
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Hydrostatic
Pressure
Osmotic
Pressure
Water and
dissolved
molecules
Water and
dissolved
molecules
b) At the capillary level
Plasma proteins account for about 1.2 mosml/L of
the total plasma osmolarity (290 mosm/L) create
an osmotic pressure about 25 – 28 mmHg, called
Osmotic Pressure
the colloid oncotic pressure, which draws water
from interstitial fluid to the capillaries
Definition
It is the pressure needed to prevent solvent migration
(osmosis).
Measurement
Water
Albumin
Osmotic Pressure
Hydrostatic
Pressure
Osmotic Pressure
Na+ =
Cl - =
Protein =
Na+ ( 150 meq/L)
Cl - (125 meq/L)
=
Organic anions
(25 meq/L)
Na+ ( 150 meq/L)
Cl - (150 meq/L)
Chemical gradient
Na+ =
Cl - =
Protein =
Na+ ( 156.5 meq/L)
Cl - (131.5 meq/L)
=
Organic anions
(25 meq/L)
_
Na+ ( 143.5 meq/L)
Cl - (143.5 meq/L)
+
_ +
_ +
_ +
_ + gradient
Chemical
_ +
_ +
_ +
Electrical
_ +gradient
Definition:
• Equilibrium that is achieved when 2 solutions
containing several ions separated by a
membrane permeable to several ions, but
not all of the ions.
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Effects :
• 1. A potential energy is
established on the
membrane due to the
presence of nondiffusable
anions on one side of the
membrane → to balance the
concentration gradient for
any ions
Effects :
2) The diffusable
ions arrange
themselves so
that their
concentrations
ratios are equal
[Na+]1
[Cl-]2
=
-]
+
[Cl
[Na ]2
1
Effects :
3) The osmotically
active particles on the
side of nondiffusable
anion are greater
than that of the other
side → there is
osmotic
dysequilibrium
I
Na+ (156.5
meq/L)
Cl - (131.5
meq/L)
Organic anions
(25 meq/L)
II
+
+ Na+ (143.5
+ meq/L)
+
+ Cl - (143.5
+ meq/L)
At Cellular Level
Biophysics , Abdelaziz Hussein
At Capillary Level
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a) At the level of cells
• Donnan equilibrium tends to cause osmotic
dysequilibrium due to the presence of
nondiffusable protein anions inside the cell→
osmosis of water inside the cell.
• This is prevented by Na-K pump→ maintain low
intracellular Na concentration → keep the inside
and outside in osmotic equilibrium.
b) At capillaries:
• Donnan equilibrium occurs in the capillaries
due to the presence of nondiffusable plasma
protein inside the capillaries, so;
• Na concentration is slightly more in the blood
than in the interstitial fluid → ↑ osmotically
active particles in blood.
• Cl concentration is relatively less in the blood
than in the interstitial fluid.
c) At glomerular capillaries:
• Donnan equilibrium causes glomerular filtrate to
contain less Na and more Cl relative to plasma.
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THANKS