OSMOSIS

Biophysics I.

Edina Szabó-Meleg, PhD University of Pécs, Medical School, Department of Biophysics 22/10/2013

OVERVIEW – DIFFUSION BROWNIAN MOTION random thermal motion of particles

DIFFUSION 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

FICK’S 2nd LAW (spatial & temporal description)

passive facilitated

transport mechanism passive active

direction chemical/electrochemical potential gradient against the chemical/electrochemical

potential gradient

mediator no ion channel carrier protein

energy requirement no yes

example O2, urea, water

Na+ glucose Na+/K+ pump

𝑱 = −𝑫∆𝒄

∆𝒙

𝑫 =𝒌𝑻

𝟔𝝅𝜼𝒓

DIFFUSION THROUGH THE CELL MEMBRANE

Onsager’s equation (linear, irreversible processes): J=XL The flow density of the extensive quantity (J) is linearly proportional to the gradient of the intensive quantity (X)

before

after (3-4 hours)

Observation: the leaf of salad becomes bigger and looks fresh again

Experiment: place a dried leaf of salade into water

OSMOSIS IN THE KITCHEN

Osmosis in the kitchen.mp4

Experiment: place an egg into corn syrup then into water

CORN SYRUP WATER

Observation : the egg shrinks Observation: the shrinked egg gains its original size, and it continues to get even bigger

before after before after

OSMOSIS

sugar solution

water before after

Experiment: fill a small-size semi-permeable bag with sugar dissolved in water, and placed in a water filled container

Observation : the bag is swelling, the water surrounding it remains pure, sugar solution has been diluted

What is the difference between the „ink” experiment and the „salade/egg/sugar” experiment?

NO TRANSPORT

1. SOLID (non-permeable) WALL (as Fick’s experiment)

OSMOSIS

x (distance)

fluid→gas (no complicated molecular interactions)

A+B components, we usually ignore one, and

examine the distribution of the other

free DIFFUSION both particles (smaller/larger) reach homogeneous distributions

2. NO WALL

OSMOSIS

x (distance)

t (t

ime)

restricted DIFFUSION: OSMOSIS smaller molecules reach a uniform distribution larger molecules remain in the compartment

3. SPECIAL WALL

OSMOSIS

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

3. SPECIAL WALL

OSMOSIS

semi-permeable membrane

OSMOSIS: unidirectional matter flow, which takes place by means of

diffusion

semipermeable wall + concentration difference

(from the perspective of osmosis, the dissolved substance’s qualities are irrelevant)

type of the wall matter transport

yes: non-permeable no

no free diffusion

yes: SEMIPERMEABLE restricted diffusion: OSMOSIS

OSMOSIS –types of walls, summary

QUANTIFICATION OF OSMOSIS

solvent

solvent + solute mixture semipermeable membrane

INJ

OUTJ

INJ

OUTJ

h

r: density h: height g = 10 m/s2

-concetration difference -semipermeable membrane: allows solvent to pass through but not the solute

-solvent flow throught the semipermeable membrane -the volume of the solvent + solute mixture increases

HYDROSTATIC PRESSURE (ph)

-solvent flow slows down

-dynamic equilibrium OSMOTIC EQUILIBRIUM

semi-permeable membrane

sugar solution

water

OSMOTIC PRESSURE

OSMOTIC PRESSURE 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

INJ

OUTJ

INJ

OUTJ

for dilute solutions and perfect semipermeable membranes using the equation of state of the ideal gas V: volume n: mole fraction T: temperature c: concentration R: universal gas constant

VAN’T HOFF’s LAW

the osmotic pressure is linearly proportional to the concentration

OSMOTIC PRESSURE

𝒑osmotic = 𝒄𝑹𝑻

𝒑ozmózis~𝒄

p2=𝑛𝑏𝑙𝑢𝑒2

𝑉𝑅𝑇

1. 2.

nblue1=nblue2

pV=nRT

p1=𝑛𝑟𝑒𝑑+𝑛𝑏𝑙

𝑢𝑒1

𝑉𝑅𝑇

p1-p2=posmosis=

𝑛𝑟𝑒𝑑𝑉

𝑅𝑇

cred

upon OSMOSIS the net particle transport occurs from the low-concentration regions (of the solute!!!!!) (low osmotic pressure) to the high-concentration regions (high osmotic pressure)

from low osmotic pressure→high osmotic pressure

it is always the more dense solution which becomes diluted

solvent solvent + solute mixture

OSMOSIS

OSMOTIC PRESSURE

1. 2.

CLASSIFYING SOLUTIONS ON THE BASIS OF OSMOTIC PRESSURE

HYPERTONIC ISOTONIC HYPOTONIC higher concentration

c > cx higher osmotic pressure

p > px

same concentration

c = cx same osmotic pressure

p = px

lower concentration

c < cx lower osmotic pressure

p < px 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

HYPERTONIC (more concentrated: 10% NaCl)

HYPOTONIC (less concentrated: 0.01% NaCl)

ISOTONIC (0.87 % NaCl)

net water OUTflux net water INflux

RED BLOOD CELLS IN DIFFERENT ENVIRONMENT

pout > pin pout = pin pout < pin

NO net water flux

HYPERTONIC HYPOTONIC IZOTONIC

RED BLOOD CELLS IN DIFFERENT ENVIRONMENT

net water OUTflux PLASMOLYSIS

plasma membrane is pulled

away from the cell wall

net water INflux TURGOR PRESSURE

plasma membrane is pushed

to the cell wall

Role of osmosis in the life of plant cells PLANT CELLS IN DIFFERENT ENVIRONMENT

NO net water flux

1. INJECTION, INFUSION drugs are dissolved in physiological saline solution isotonic environment (compared to the body fluid)

2. 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 areas)

induces water outflow from the swollen areas reduced swelling

3. 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

OSMOSIS IN THE MEDICAL PRACTICE

hypertonic

water influx

hypertonic

water outflow

different particles can be sorted by semipermeable membranes pore size of the membrane determines which molecules can pass

through the membrane

t = 0 s t

4. DIALYSIS

dialysis bag

semipermeable membrane

concentrated solution

OSMOSIS IN THE MEDICAL PRACTICE

protein products toxins other waste products

treatment of patient with severe kidney disease remove soluble chemicals toxic for the body (protein products, toxins, other waste

products exit with water, essential plasma proteins, cellular elements of blood remain),

4.1. HAEMODIALYSIS

Schematic diagram of haemodialysis („artificial kidney” instrument).

OSMOSIS IN THE MEDICAL PRACTICE

essential element:long semi-permeable membrane (cellophane), surrounded by dial.solution average treatment time: 4-8 h dial.solution has to be changed frequently

check ion-concentrations and metallic-ion-contaminations in the solution

OVERVIEW

• Osmosis

• Van’t Hoff’s law

• Osmotic pressure and its significance (rbc, medical application)