9. Water Transport

Front 1

What is the permeability of water relative to other hydrophilic diffusing molecules?

Back 1

Much more permeable (than for e.g. urea)

Front 2

Why is water so much more permeable than other aqueous molecules?

Back 2

Because it diffuses in 2 ways:
1. Passive diffusion between lipids
2. Via aquaporin channels

Front 3

How do glycerol and urea get through the cell membrane?

Back 3

By protein channels

Front 4

Define Osmosis:

Back 4

Displacement of vol due to net movement of water down its concentration gradient across a SEMIPERMEABLE membrane separating 2 comparments of unequal water concentrations.

Front 5

What does osmotically active mean?

Back 5

A semipermeable membrane is not permeable to that electrolyte (e.g. Na and Cl)

Front 6

If a solution has an osmolyte conc of 0, then what is it?

Back 6

Pure water w/ a concentration of 55.5 Molal

Front 7

How is osmosis of water different from simple diffusion?

Back 7

Simple diffusion results in no net vol displacement - b/c the membrane is permeable to water AND ions in such a case.

Front 8

Define osmotic pressure:

Back 8

The countering HYDROSTATIC pressure that would be required to prevent a change in compartment volume from which water flows.

Front 9

What type of property is osmotic pressure?

Back 9

Colligative

Front 10

What 2 factors determine Osmotic pressure?

Back 10

1. Molar fractions of solute and solvent in ea compartment
2. Deg. of solute aggregation and dissolution in solvent.

Front 11

Equation that gives osmotic pressure:

Back 11

Vant hoff equation

Front 12

What is the Vant Hoff equation?

Back 12

pi = nRT (Ci - Co)

Front 13

What are the 2 ideal system requirements of Vant Hoff's eqn?

Back 13

1. Semipermeable membrane is only permeable to water
2. All solute particles completely dissociate.

Front 14

What would be the osmotic pressure of a 1 molar difference in concentration?
( in atm and in mm Hg)

Back 14

25.4 atm

19,304 mm Hg

Front 15

What is psi?

Back 15

The osmotic coefficient

Front 16

What is the range of the osmotic coefficient psi?

Back 16

0 to 1 (unity)

Front 17

What is the purpose of the osmotic coefficient?

Back 17

It describes the extent of aggregation of solute particles in solution - how dissociated they are.

Front 18

How do you calculate osmolarity?

Back 18

(psi) x Valence x [solute]

Front 19

Why do we care about Vant Hoff's eqn and osmolarity?

Back 19

So that we can calculate how much salt to put into saline so we don't kill patients with IV.

Front 20

For mammalian blood plasma:
-What is osmotic pressure?
-What is osmolarity?
-What is osmolality?

Back 20

pi = 7.29 atm (5540.4 mm Hg)
Osmolarity = 286 mOsm
Osmolality = 290 mOsm

Front 21

What is the concentration of NaCl in an isosmotic solution?

Back 21

154 mM

Front 22

What is the osmolarity coefficient of NaCl?

Back 22

0.93

Front 23

What does the osmolarity coefficient do to the calculation of osmolarity?

Back 23

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!

Front 24

What MUST a cell's INTRACELLULAR OSMOLAR CONCENTRATION be in order for it to maintain normal volume?

Back 24

286 Mosmolar (290 mosmolal)

Front 25

What is Tonicity?

Back 25

The effect that a physiological salt solution has on the volume of a biological cell placed within it.

Front 26

What is an Isotonic solution?

Back 26

Soln w/ osmolyte concentration just sufficient to maintain a cell at its NORMAL in vivo volume.

Front 27

What is a Hypotonic solution?

Back 27

A soln w/ osmolyte concentration
that cause the cell vol to increase, swell, maybe burst.

Front 28

Why do cells burst in hypotonic solution?

Back 28

Because the solution has lower solute concentration, so water wants to go where salt is, which is inside the cell.

Front 29

What is the calculation for a PSS that is isotonic to cells?

Back 29

Osm = 0.93 x 2 x 154

Front 30

What is the water concentration of a hypotonic solution compared to that in the cell?

Back 30

Greater

Front 31

What is the limit of hypotonicity at which a RBC placed in solution will burst?

Back 31

1.6 x normal osmolarity

Front 32

What are the consequences of putting a cell in pretty hypotonic solution?

Back 32

-Cell swells and can lyse
-Permeability increases for all intracellular solutes
-Equilibration of all molecules

Front 33

What happens to a cell placed in hypertonic solution?

Back 33

Crenation - water leaves and it shrinks, leaving too much membrane relative to its volume.

Front 34

What happens when a RBC is placed in solution of 2x normal osmolarity due to glycerol?

Back 34

Initial: cell will shrink due to hypertonicity
Then: glycerol is slowly permeable so equilibrium will be reached and cell size returns to normal.

Front 35

How much NaCl + Glycerol make a 2x isosmotic solution?

Back 35

154 mM NaCl (2x.93x154 = 286)
300 mM Glycerol

Front 36

Is a solution with 300 mOsm glycerol isotonic with a cell?

Back 36

NO - because glycerol is not an osmolyte; it is permeable to the membrane.

Front 37

How would you describe a solution with 300 mOsm glycerol and 154 mM NaCl?

Back 37

Init: Isotonic and Hyperosmotic
-after glycerol equilibrates-
Then: Isotonic and Isosmotic

Front 38

What is Qv?

Back 38

Volume flow of solvent

Front 39

What forces act to cause Qv?

Back 39

-Hydrostatic pressure
-Osmotic pressure

Front 40

What is the equation for Qv?

Back 40

Qv = Kf x Pgradient

Front 41

What is Kf?

Back 41

Filtration coefficient

Front 42

2 Factors that determine Kf:

Back 42

1. Cell wall permeability
2. Effective surface area

Front 43

What is the Pgradient?

Back 43

The hydrostatic force gradient

Front 44

What is the Qv equation used mainly for?

Back 44

Transcapillary flow

Front 45

Can water move up its concentration gradient?

Back 45

Yes