Download - 010-Membrane Transport 2
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Processes by WhichParticles Move AcrossCell Membranes
Membrane Transport
Osmosis: Definition
The flow of water across a semipermeablemembrane from a compartment in which the soluteconcentration is lower to one in which the soluteconcentration is greater
A semipermeable membrane is defined as amembrane permeable to water but impermeable tosolutes
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Osmosis
The left chamber contains asolution
The right chamber containspure water
Water will flow by osmosisfrom the pure water chamberinto the solution
Schematic Representation of the Definition
of Osmotic Pressure of a Solution
The osmotic pressure of asolution can be obtained by
determining the pressurethat must be applied to a
solution to prevent waterfrom entering it across anideal semipermeablepermeable
When the hydrostaticpressure applied to thesolution in chamber A isequal to the osmoticpressure of that solution,
there will be no net waterflow across themembrane
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Colligative Properties of a Solution
Properties of a solution that depend on theconcentration of the solute present rather thanon its chemical nature
Colligative properties of a solution:
vapor pressure
freezing point
boiling point
osmotic pressure
Computing the Osmotic Pressure of a
Solution
1. Vant Hoffs Law for calculation of osmotic pressure
2. Use of freezing point depression for estimation ofosmotic pressure
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Illustration of Osmotic Pressure
The concentration of water in the leftcompartment is less than in the rightcompartment
There is a concentration gradientfor water
Water moves in the tube from right toleft
Water continues to move from the regionof high water concentration to theregion of low water concentrationUNTIL the difference in height betweenthe 2 columns of water is 26 cm
At this height, a column of water exerts a
hydrostatic pressure (P) that is equal tothe difference between the osmotic
pressures ( ) of the 2 solutionsPhydrostatic = L- R
Vant Hoffs Law
= RT( i c) Osmotic pressureR Ideal gas constantT Absolute temperature
Osmotic coefficient i Number of particles formed by dissociation
of a solute molecule
c Molar concentration of a solute (moles ofsolute/liter of solution)
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
The Osmotic Coefficient ()
depends on the:nature of the solute
concentration of the solute
Values of may begreater than 1
less than 1
values can be obtained from handbooks thatlist values of for different substances asfunctions of concentration
Osmotic Coefficients of Certain Solutes of
Physiological Interest
values for solutes of physiological importance apply toconcentrations of these solutes in the extracellular fluids ofmammals
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
The Osmotic Pressure of a Solution
The osmotic pressure of a solution depends on thenumber of particles in solution (i)
Every solute particle in solution contributes to theosmotic pressure
The degree of ionization of a solute must be takeninto account when calculating osmotic pressure
The Osmotic Pressure of a Solution
= RT( i c) The osmotic pressure of a solution is often referred
to as osmolarity
(ic) can be regarded as the osmotically effectiveconcentration of the solution
(ic) is called the osmolarity of the solution (ic) is expressed in osmoles/liter Sometimes, a less precise estimate of osmotic
pressure is computed assuming that is equalto 1
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8/8/2019 010-Membrane Transport 2
7/16
University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Sample Calculations
1. What is theosmotic pressureat 0oC of a 154mMNaCl solution? Use=0.93 for NaCl
2. What is theosmolarity of thissolution?
1. = RT( i c) = 22.4 L.atm/mole x 0.93 x 2
x 0.154 mole/L = 6.42 atm
2. Osmolarity = ( i c)( i c)= 0.93 x 2 x 0.154
mole/L
( i c)= 0.286 osmole/L = 286
mOsmole/L
Sample Calculation
Sometimes, a less precise estimate of osmotic pressureis computed assuming that is equal to 1
1 mole of NaCl is dissolved in 1 liter of solution.
What is the osmotic pressure of the solution?
The salt will dissociate into 1 mole of Na+ and1mole of Cl-
The osmotic pressure of the solution will be 2osmoles/L:
1 osmole/L contributed by Na+
1 osmole/L contributed by Cl-
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Depression of Freezing Point of Water by Solute
ic = Tf /1.86 ic osmolarity of solution Tf freezing point depression in 0C
A 1 osmolar solution has an osmotic pressure of22.4 atm at 00C and freezes at 1.860C
Isosmotic / Hypoosmotic/ Hyperosmotic
Solutions
Solutions A and C areisosmotic
Solutions A and C arehypoosmotic with respectto solution B
Solution B is hyperosmoticwith respect to solutions Aand C
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Water Permeability of a Cell
Biological membranes are verypermeable to water
A change in soluteconcentration will cause water tomove and abolish any differencein osmotic pressure between 2compartments
As a result, athough theconcentrations and types ofsubstances in the intracellularand extracellular
compartments DIFFERsignificantly, the osmolarity ofthese compartments is thesame
Tonicity of a Solution Determined by the response of a cell when it is placed
in the solution Consider the response of a red blood cell when it is
placed in 3 different types of solutionsRBCs are convenient to use because they can be
isolated and observed If a RBC swells and stays swollen or (bursts) when
placed in a particular solution, that solution is said tobe hypotonic
If a RBC shrinks and stays shrunken when placed in a
particular solution, that solution is said to behypertonic If the volume of a RBC stays the same when added to
a particular solution, that solution is said to beisotonic
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Osmotic Behavior of RBCs
A RBC is placed in a solution containing 0.25M sucrose, a solutionthat is isosmotic with the intracellular milieu of the RBC
Sucrose cannot penetrate the cell membrane (impermeantsolute)
Most of the solutes found within the RBC are alsomembrane impermeant
The RBC will:
Shrink?
Swell?
Maintain a constant volume?
The RBC is placed in a solution that is:
Hypertonic? Hypotonic?
Isotonic?
Osmotic Behavior of RBCs
A RBC is placed in a solution containing 0.25M urea, a solution that
is isosmotic with the intracellular milieu of the RBC.
Urea is a permeant solute
Typically, there is very little urea inside the RBC
Most of the solutes found within the RBC are membraneimpermeant
The RBC will:
Shrink?
Swell?
Maintain a constant volume? The RBC is placed in a solution that is:
Hypertonic?
Hypotonic?
Isotonic?
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Osmotic Behavior of RBCs
A RBC is placed in a solution containing 0.5M sucrose, a solutionthat is hyperosmotic with the intracellular milieu of the RBC
Sucrose cannot penetrate the cell membrane (impermeantsolute)
Most of the solutes found within the RBC are alsomembrane impermeant
The RBC will:
Shrink?
Swell?
Maintain a constant volume?
The RBC is placed in a solution that is:
Hypertonic? Hypotonic?
Isotonic?
Clinical Correlation
Isotonic NaCl solution, also known as isotonic saline, isused for intravenous rehydration or for administration ofdrugs to patients
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Osmotic Effects of Solutes
Magnitude of OsmoticFlows
Rate of Osmotic Flow Caused by Permeating
Solutes
When a difference of hydrostatic pressure (P) causeswater to flow across a membrane, the rate of water flow(Vw) is:
Vw = L P L is a constant of proportionality, called the hydraulic
conductivity
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Reflection Coefficients
Vw = L is the reflection coefficient
is a dimensionless number that ranges from 1 forcompletely impermeant solutes to 0 for extremelypermeant solutes.
Value of is a property of a particular solute and aparticular membrane
Osmotic Water Flow Across a Porous Dialysis Membrane
Induced by Solutes of Different Molecular Size
Flow is expressed as microliter/min caused by a 1M-concentrationdifference of solute across the membrane
The solutions have identical freezing points so the total osmotic pressuresare the same
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
OsmosisPag
Question
Two compartments of equal volume areseparated by a solid partition containing ahole with an area of 2 cm. A stopperinitially occludes the hole. The
compartments have rigid walls and aretotally filled with a solution containingCaCl2 and sucrose in the concentrations
shown in the figure. Simple diffusion is theonly process by which Ca2+ and Cl- cross
the membrane.
Calculate the osmotic pressure (in
osmoles) of the solution (either in #1 or#2) that is hypoosmotic with respect
to the solution on the other side of themembrane before the stopper isremoved from the hole in the partition.
Answer
The solution with thelower osmolarity, theHYPOOSMOTICsolution, will be incompartment #2
There are fewerparticles on thisside of themembrane
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University of Balamand
Faculty of Medicine and Medical Sciences
Dr. M. Khachab
GPHY 402
September 7, 20
Membrane Transport
Osmosis
Reference
Chapter 4: Transport of Ions and Molecules Through theCell Membrane inTextbook of Medical Physiology byGuyton and Hall
Chapter 11: Transport of Small Molecules and ElectricalProperties of the Cell Membrane inCell by Alberts,Johnson, Lewis, Raff, Roberts and Walter