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45 Cards in this Set

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  • Back
What is the permeability of water relative to other hydrophilic diffusing molecules?
Much more permeable (than for e.g. urea)
Why is water so much more permeable than other aqueous molecules?
Because it diffuses in 2 ways:
1. Passive diffusion between lipids
2. Via aquaporin channels
How do glycerol and urea get through the cell membrane?
By protein channels
Define Osmosis:
Displacement of vol due to net movement of water down its concentration gradient across a SEMIPERMEABLE membrane separating 2 comparments of unequal water concentrations.
What does osmotically active mean?
A semipermeable membrane is not permeable to that electrolyte (e.g. Na and Cl)
If a solution has an osmolyte conc of 0, then what is it?
Pure water w/ a concentration of 55.5 Molal
How is osmosis of water different from simple diffusion?
Simple diffusion results in no net vol displacement - b/c the membrane is permeable to water AND ions in such a case.
Define osmotic pressure:
The countering HYDROSTATIC pressure that would be required to prevent a change in compartment volume from which water flows.
What type of property is osmotic pressure?
What 2 factors determine Osmotic pressure?
1. Molar fractions of solute and solvent in ea compartment
2. Deg. of solute aggregation and dissolution in solvent.
Equation that gives osmotic pressure:
Vant hoff equation
What is the Vant Hoff equation?
pi = nRT (Ci - Co)
What are the 2 ideal system requirements of Vant Hoff's eqn?
1. Semipermeable membrane is only permeable to water
2. All solute particles completely dissociate.
What would be the osmotic pressure of a 1 molar difference in concentration?
( in atm and in mm Hg)
25.4 atm

19,304 mm Hg
What is psi?
The osmotic coefficient
What is the range of the osmotic coefficient psi?
0 to 1 (unity)
What is the purpose of the osmotic coefficient?
It describes the extent of aggregation of solute particles in solution - how dissociated they are.
How do you calculate osmolarity?
(psi) x Valence x [solute]
Why do we care about Vant Hoff's eqn and osmolarity?
So that we can calculate how much salt to put into saline so we don't kill patients with IV.
For mammalian blood plasma:
-What is osmotic pressure?
-What is osmolarity?
-What is osmolality?
pi = 7.29 atm (5540.4 mm Hg)
Osmolarity = 286 mOsm
Osmolality = 290 mOsm
What is the concentration of NaCl in an isosmotic solution?
154 mM
What is the osmolarity coefficient of NaCl?
What does the osmolarity coefficient do to the calculation of osmolarity?
For NaCl, it means only 93% of the solute is dissolved - so the actual osmolarity is lower than you would think if it were 100% dissolved!
What MUST a cell's INTRACELLULAR OSMOLAR CONCENTRATION be in order for it to maintain normal volume?
286 Mosmolar (290 mosmolal)
What is Tonicity?
The effect that a physiological salt solution has on the volume of a biological cell placed within it.
What is an Isotonic solution?
Soln w/ osmolyte concentration just sufficient to maintain a cell at its NORMAL in vivo volume.
What is a Hypotonic solution?
A soln w/ osmolyte concentration
that cause the cell vol to increase, swell, maybe burst.
Why do cells burst in hypotonic solution?
Because the solution has lower solute concentration, so water wants to go where salt is, which is inside the cell.
What is the calculation for a PSS that is isotonic to cells?
Osm = 0.93 x 2 x 154
What is the water concentration of a hypotonic solution compared to that in the cell?
What is the limit of hypotonicity at which a RBC placed in solution will burst?
1.6 x normal osmolarity
What are the consequences of putting a cell in pretty hypotonic solution?
-Cell swells and can lyse
-Permeability increases for all intracellular solutes
-Equilibration of all molecules
What happens to a cell placed in hypertonic solution?
Crenation - water leaves and it shrinks, leaving too much membrane relative to its volume.
What happens when a RBC is placed in solution of 2x normal osmolarity due to glycerol?
Initial: cell will shrink due to hypertonicity
Then: glycerol is slowly permeable so equilibrium will be reached and cell size returns to normal.
How much NaCl + Glycerol make a 2x isosmotic solution?
154 mM NaCl (2x.93x154 = 286)
300 mM Glycerol
Is a solution with 300 mOsm glycerol isotonic with a cell?
NO - because glycerol is not an osmolyte; it is permeable to the membrane.
How would you describe a solution with 300 mOsm glycerol and 154 mM NaCl?
Init: Isotonic and Hyperosmotic
-after glycerol equilibrates-
Then: Isotonic and Isosmotic
What is Qv?
Volume flow of solvent
What forces act to cause Qv?
-Hydrostatic pressure
-Osmotic pressure
What is the equation for Qv?
Qv = Kf x Pgradient
What is Kf?
Filtration coefficient
2 Factors that determine Kf:
1. Cell wall permeability
2. Effective surface area
What is the Pgradient?
The hydrostatic force gradient
What is the Qv equation used mainly for?
Transcapillary flow
Can water move up its concentration gradient?