Lecture 4 Flashcards
Explain water transport?
Water transport is completely passive
No water pumps exist
Water passes into cell with the use of aquaporins
simple diffusion = no saturation but has linear kinetics
What is the definition of concentration?
the mass of a substance in a known volume
How does water move?
Water can move across membranes and it is going to do so by going down its concentration gradient.
Water will move in the direction of high solute concentration until equilibrium.
What are the two driving forces of water movement?
- Osmotic force- water wanting to move to an area of high solute
- Hydrostatic driving forces- the effect of gravity on the fluid across capillary endothelial cells
What is the van’t Hoff equation?
This equation is used to calculate the osmotic pressure of a solution.
pie = nRTC
What is water flux and what is the equation?
A difference in osmotic pressure between two compartments that leads to water movement
Jv = Kh A [RC (Ci - Co)]
Describe osmosis?
The flow of water between two solutions that are separated by a semi-permeable membrane
water will flow from low osmolarity to high osmolarity
What does the reflection coefficient (RC) represent?
it is a number between 0 and 1
0 indicates that the solute is totally permeable and exerts NO osmotic pressure differences
1 indicates that the solute is totally impermeable and therefore exerts an osmotic pressure on water flow.
How is osmolarity different from tonicity?
Osmolarity is the total concentration of all particles in the solution
on the other hand, tonicity is only the concentration of active particles.
What kind of particles contribute to tonicity?
ONLY impermeable particles will contribute to the tonicity and cause changes in cell volume
What describes the volume change of a cell at equilibrium?
tonicity
Net water movement will be into the compartment that has the higher concentration of non-penetrating solutes.
What kinds of solutes can penetrate the membrane?
glucose, urea, and glycerol
solutes will distribute to equilibrium
What kinds of solutes cannot penetrate the membrane ?
sucrose, NaCl, KCl
water will move in to dilute solutes
these solutes determine tonicity!!!
Explain iso-osmotic, hyperosmotic, and hypo-osmotic?
iso-osmotic is when the osmotic pressure is equal in both the solution and cell
hyperosmotic is when the solution has a greater osmotic pressure than the cell
hypo-osmotic pressure is when the solution has a less osmotic pressure compared to the cell
Explain isotonic, hypertonic, and hypotonic?
isotonic is when the cell is at equilibrium and will not shrink or swell
hypertonic is when the cell shrinks because the non-penetrating solute concentration on the outside of the cell is greater than inside the cell
hypotonic is when the cell swells because the non-penetrating solute concentration on the outside of the cell is less than inside the cell
150 mM of NaCl + 50 mM of glycerol
osmolarity? tonicity? water movement?
150 x 2 = 300 + 50 x 1 = 350
350 means hyperosmotic because normal is between 290 and 300
NaCl is cannot cross and glycerol can
the tonicity is isotonic because the NaCl osomolarity is 300 (normal)
The cell will, at first, shrink because water leaves cell but the glycerol will equilibrate and attract water (cell return to normal size)
170 mM NaCl + 10mM glycerol
osmolarity? tonicity? water movement?
170 x 2 = 340 + 10 x 1 = 350
Hyperosmotic!
340 (NaCl) to high! Thus hypertonic
Water will leave the cell. glycerol affect on equilibrium is minimal!
75 NaCl + 10 mM glycerol
osmolarity? tonicity? water movement?
75 x 2 =150 + 10 x 1 =160
hypo-osmotic!!!
150 (NaCl) = hypotonic!
Water will enter cell
All hypo-osmotic solutions are?
hypotonic
iso-osmotic solutions can be?
hypotonic or isotonic
hyperosmotic solutions can be?
hypo, hyper, or isotonic
5 percent dextrose in water
isotonic, but physiologically hypotonic
10 percent dextrose in water
hypertonic
0.45 percent saline
hypotonic
0.9 percent saline
isotonic
3.0 percent saline
hypertonic
why use 5 percent dextrose in water?
Used to replace water loss and treat hypernatremia
170 cal and no electrolytes
why use 10 percent dextrose in water?
provides free water
340 cal and no electrolytes
why use 0.45 percent saline?
provides free water in addition to Na and Cl
used to replace hypotonic fluid loss
no cals
why use 0.90 percent saline?
Used to expand intravascular volume and replace extracellular fluid loss
does not provide free water
may cause intravascular overload and hyperchloremic acidosis
why use 3.0 percent saline?
Used to treat symptoms of hyponatremia
must be given slowly and with caution because it could lead to intravascular fluid overload and pulmonary edema
