Biophysics I - OSMOSIS
11/09/2012
Biophysics I. - OSMOSIS
BROWNIAN MOTION
OVERVIEW – DIFFUSION
random thermal motion of particles
DIFFUSION
Biophysics I.
DIFFUSION – OSMOSIS
due to the non-uniform (inhomogeneous) distribution of particles
net transport of particles (Brownian motion) occurs from a region of higher concentration to a region of
lower concentration
which continues until the distribution of particles is uniform (homogeneous)
FICK’S 1st LAW (spatial description)
∆
∆
DIFFUSION COEFFICIENT: Stokes-Einstein equation
11th September 2012
Dr. Beáta Bugyi
University of Pécs, Medical School
Department of Biophysics
FICK’S 2nd LAW (spatial & temporal description)
DIFFUSION THROUGH THE CELL MEMBRANE
OSMOSIS – EXPERIMENT 1
Experiment 1: place a dried leaf of salade into water
Biophysics I. - OSMOSIS
OSMOSIS – EXPERIMENT 2
Biophysics I. - OSMOSIS
Experiment 2: place an egg into corn syrup then into water
before
CORN SYRUP
WATER
after (3-4 hours)
Observation : the egg shrinks
before
after
Observation: the shrinked egg gains
its original size, and it continues to get
even bigger
before
after
Observation: the leaf of salad becomes bigger and looks fresh again
OSMOSIS
Biophysics I. - OSMOSIS
What is the difference
between the „ink” experiment and the „salade/egg” experiment?
Biophysics I. - OSMOSIS
1. SOLID (non-permeable) WALL
NO TRANSPORT
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Biophysics I - OSMOSIS
11/09/2012
Biophysics I. - OSMOSIS
Biophysics I. - OSMOSIS
2. NO WALL
3. SPECIAL WALL
SEMIPERMEABLE – „filter”
allows smaller slovent molecules to pass through, but not the larger solute molecules
PORE SIZE SELECTIVITY
animal skin pellicles, walls of living cells, ceramic plate with holes, cellophane
free DIFFUSION
both particles (smaller/larger) reach homogeneous distributions
Biophysics I. - OSMOSIS
3. SPECIAL WALL
Biophysics I. - OSMOSIS
type of the wall
matter transport
yes: non-permeable
no
no
free diffusion
yes: SEMIPERMEABLE restricted diffusion: OSMOSIS
OSMOSIS
unidirectional matter flow, which takes place by means of
diffusion
semipermeable wall + concentration difference
restricted DIFFUSION: OSMOSIS
smaller molecules reach a uniform distribution
larger molecules remain in the compartment
QUANTIFICATION OF OSMOSIS
Biophysics I. - OSMOSIS
≫ J OUT
J OUT
J IN
J IN
solvent
semipermeable membrane
concetration difference
semipermeable membrane:
allows solvent to pass through but
not the solute
Biophysics I. - OSMOSIS
OSMOTIC PRESSURE
h
J OUT
J OUT
J IN
J IN
solvent
+ solute
mixture
solvent flow throught the
semipermeable membrane
the volume of the solvent +
solute mixture increases
HYDROSTATIC PRESSURE
(ph)
solvent flow slows down
ρ: density
h: height
g = 10 m/s2
OSMOTIC PRESSURE
dynamic equilibrium
OSMOTIC EQUILIBRIUM
pressure that has to be exerted on the solution connected to pure solvent by a
semipermeable membrane to reach dynamic equilibrium, to counteract osmosis
pressure that inhibits the net solvent flow
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Biophysics I - OSMOSIS
11/09/2012
OSMOTIC PRESSURE
Biophysics I. - OSMOSIS
OSMOTIC PRESSURE
Biophysics I. - OSMOSIS
VAN’T HOFF’s LAW
for dilute solutions and perfect semipermeable membranes using the equation of state of the
ideal gas
→
!"#$% upon OSMOSIS the net particle transport occurs from the lowconcentration regions (of the solute!!!!!) (low osmotic pressure) to the
high-concentration regions (high osmotic pressure)
V: volume
n:: mole fraction
T: temperature
c: concentration
R: universal gas constant
it is always the more dense solution which becomes diluted
OSMOSIS
~
solvent
+ solute
mixture
the osmotic pressure is linearly proportional to the concentration
solvent
Biophysics I. - OSMOSIS
CLASSIFYING SOLUTIONS ON THE BASIS OF OSMOTIC PRESSURE
comparision of solutions!
HYPERTONIC
ISOTONIC
HYPOTONIC
higher concentration
same concentration
lower concentration
c > cx
c = cx
c < cx
higher osmotic pressure
same osmotic pressure
lower osmotic pressure
p = px
p < px
p > px
SOLUTE
- / 0
-#!"#!%! / 0#!"#!%!
Biophysics I. - OSMOSIS
RED BLOOD CELLS IN DIFFERENT ENVIRONMENT
HYPERTONIC
(more concentrated: 10% NaCl)
ISOTONIC
(0.87 % NaCl)
pout > pin
pout = pin
HYPOTONIC
(less concentrated: 0.01% NaCl)
pout < pin
for the cells of the human
body, blood:
0.87 % (0.15 M) NaCl
physiologic saline solution
3.8 % sodium citrate
5.5 % (0.3 M) glucose
x: reference
RED BLOOD CELLS IN DIFFERENT ENVIRONMENT
net water OUTflux
NO net water flux
Biophysics I. - OSMOSIS
net water INflux
Biophysics I. - OSMOSIS
PLANT CELLS IN DIFFERENT ENVIRONMENT
HYPERTONIC
HYPERTONIC
ISOTONIC
HYPOTONIC
ISOTONIC
(0.87 % NaCl)
net water OUTflux
PLASMOLYSIS
NO net water flux
net water INflux
TURGOR PRESSURE
HYPOTONIC
plasma membrane is pulled
away from the cell wall
plasma membrane is pushed to
the cell wall
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Biophysics I - OSMOSIS
11/09/2012
Biophysics I. - OSMOSIS
OSMOSIS IN THE MEDICAL PRACTICE
OSMOSIS IN THE MEDICAL PRACTICE
Biophysics I. - OSMOSIS
DIALYSIS
INJECTION, INFUSION
drugs are dissolved in physiological saline solution
isotonic environment (compared to the body fluid)
water outflow
different particles can be sorted by semipermeable membranes
pore size of the membrane determines which molecules can pass through the
membrane
TREATMENT OF OEDEMAS, INFLAMED AREAS
abnormal accumulation of fluid beneath the skin or in one or
more cavities of the body that produces swelling (fluid
accumulation)
dextran-solution/bitter salt (MgSO4-solution)-based treatment
hypertonic environment is created (compared to the swollen
hypertonic
areas)
induces water outflow from the swollen areas
water influx
reduced swelling
dialysis bag
semipermeable membrane
concentrated solution
TREATMENT OF CONSTIPATION - LAXATIVE SALTS
laxative salts are not absorbed by the large intestine
hypertonic environment is created in the large intestine
results in water influx into the large intestine
dilution of colonic content, facilitated excretion
hypertonic
OSMOSIS IN THE MEDICAL PRACTICE
HAEMODIALYSIS
treatment of patient with severe kidney disease
remove soluble chemicals toxic for the body
Schematic diagram of haemodialysis.
t=0s
Biophysics I. - OSMOSIS
t
Biophysics I. - OSMOSIS
OVERVIEW – the most important things
Osmosis
Van’t Hoff’s law
Osmotic pressure and its significance
protein products
toxins
other waste products
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