Cell Volume Regulation Flashcards
In discussions of cell volume changes, we consider only
fluctuations in water content.
Water diffuses in a given direction in order to equilibrate differences in _____
osmolarity
If the osmolarity outside of a cell is greater than the osmolarity inside the cell,
water will diffuse out of the cell and the cell will shrink.
In this case, the extracellular fluid is said to be hyper osmotic and hypertonic to the cell
If the osmolarity of a cell is less than the osmolarity inside the cell,
water will diffuse into the cell and the cell will swell.
In this case, the extracellular fluid is said to be hypo osmotic and hypotonic to the cell
List the three mechanisms that different cells have evolved to keep from swelling and bursting.
- make the cell membrane membrane impermeable to water
a. creates a problem for growing cells - build a strong cell wall
a. applies hydrostatic force to counter osmotic force
b. requires significant forces and limit allowed cell shapes - balance osmotic force by having solute molecule in the extracellular fluid
a. functions to equilibrate the osmolarities inside and outside the cell
If a cell is put in solution with a higher concentration of the permeable solute glycerol:
- initially the osmolarity is much greater outside the cell and water flows out of the cell
- at the same time, glycogen is moving down its concentration gradient into the cell
- eventually, glycogen will build up in the cell and the osmolarity will become greater inside the cell
- water will then diffuse into the cell causing it to swell
In cases where there is a permeating solute, the permeating solute will _______
diffuse across the membrane from higher concentration to lower concentration.
If the osmolarity is greater outside the cell, water will flow
out of the cell.
If the osmolarity is greater inside the cell, _______
water will flow into the cell.
In either case, water is diffusing in one direction or another in order to dilute solutes and achieve equilibrium.
the presence of the nonpermeating molecules inside the cell will reduce the probability
the probability that a water molecule will leave the cell, and this means more water will enter than will leave.
This net inward movement of water across a semi-permeable membrane (i.e., a membrane permeable to solvent, but not to solute) is called
osmosis.
Cell volume depends only on
the movement of water
real cells can’t swell beyond about ____% of their resting volume
140
The exact time course of volume change will depend on how
how easily (relative to water) the solute can cross the membrane.
Another consequence of a permeating solute is that ____________.
it will not exert as large an osmotic force as a nonpermeating solute at the same concentration
The Van’t Hoff equation, relates _______
osmotic pressure to hydrostatic pressure,
Diffusion refers to
the random thermally-agitated movement of molecules from regions of higher concentration to regions of lower concentration.
Osmosis refers to
the diffusion of water.
osmolarity
osM
osmoses of solute per liter
an osmole is the number of osmotically active particles
this is the number of ions/particles present when a compound is dissolved in water
Molar equivalents (mEq)
amount of substrate needed to react with or supply one mole of hydrogen ions in an acid base reaction
refer individuals ion concentration
tonicity
measure the osmotic pressure between two solutions separated by a membrane and determine whether a cell will shrink or swell
hypotonic solution makes cell
swell
hypertonic solution makes a cell
shrink
isotonic solution results in
no change in cell volume
Osmosis occurs at a _______ than simple diffusion because ________
faster rate
of the effect of nonpermeable solutes.
water movement into the cell causes
the cell to swell, and unless some countering force is applied, the plasma membrane will be stretched and eventually will rupture.
How much the osmotic pressure is diminished depends on________
how easily the molecule can cross the membrane, relative to water.
When only nonpermeable solutes are present the osmotic pressure in a system is described by the following equation:
π =RT∆C
However, when the solute present is permeant to the membrane, the _______ is diminished. The degree to which the osmotic pressure is diminished depends on ______.
osmotic pressure
how permeable the membrane is to the solute relative to water
The equation for osmotic pressure is modified to reflect this effect:
π =oRT∆C
Where o is the reflection coefficient, ranging from 0 to 1. Where 0 is used for a solute that is as permeant as water and 1 is for a solute that is completely nonpermeant.
A molecule that crosses half as easily as water will exert _______
half of the ideal osmotic pressure of a non-permeating solute.
