DSA osmolarity and osmolality

Question 1

• Diffusion:

Answer 1

o Movement of the solute across a membrane when there is a concentration gradient.
o Moves from high concentration to low concentration.
o The “default” event if possible.

Question 2

• Osmosis

Answer 2

o Movement of the solvent
o Result of pressure gradient.
o Only if the solvent can’t move.
o If osmosis occurs, the volume of both compartments can change markedly.

Question 3

what is the solvent in the body

Answer 3

water

Question 4

what is the solute in the body

Answer 4

ions, proteins, other substances

Question 5

osmolarity equation

Answer 5

Osmolarity = g x [C]

1. the molar concentration of the solute [C]
2. the number of particles the solute dissociates into when place in solution (g).

Question 6

what has a g=1

Answer 6

if the solute doesn't dissociate 
	examples:   
	glucose
	urea
	proteins

Question 7

what has a g>1

Answer 7

the solute dissociates when placed in solution.
 Examples include:
 NaCl
 g = 2 if the NaCl were to completely dissociate into Na and Cl.
 the measured g = 1.8 because not all the NaCl dissociates.
 CaCl2
 g = 3 at the maximum, but again dissociation is not complete in water.

Question 8

if the reflection coefficient is 0

Answer 8

• The solute is completely permeable to the membrane (I’ve already said this).
• The osmotic pressure is 0 (g[C] X 0RT = 0!)
• Therefore the solute will diffuse across the membrane
• There will be no volume change.

Question 9

if the reflection coefficient is 1

Answer 9

• the solute cannot cross the membrane,
• the osmotic pressure is “high”,
• Osmosis will occur
• the volume will increase proportionate to the water motion.

Question 10

what is the average osmolarity of the ICF and ECF of the human body

Answer 10

290 mOsm.

The normal range is 270 - 300 mOsm

Question 11

what % sodium choloride solution is isosmotic to RBC

Answer 11

0.9%

Question 12

how do you calculate osmolality of plasma

Answer 12

Estimated Osmolality = (2x [Na]) + ([glucose]/18) + ([BUN}/2.8)

Question 13

• Isosmotic solutions

Answer 13

cause no change in a cell’s volume because there is no gradient for water to move

Question 14

hyposmotic solution

Answer 14

o is one in which there is a higher water “concentration” than we find in the cell
o There is a gradient for water to move
o So the cell will swell or rupture.

Question 15

hyperosmotic solution

Answer 15

o is one in which the osmolarity of the solution is greater than that in the cell.
o there is less water outside the cell
o The water moves from the cell to the solution
o The cell will shrink, aka crenate.

Question 16

tonicity

Answer 16

is determined by the cell’s response to being put into the solution, not the numbers

Question 17

isotonic

Answer 17

the cell didn’t change volume

Question 18

hypotonic

Answer 18

• the cell swelled or lysed due to swelling as water moved into the cell.

Question 19

o hypertonic

Answer 19

water moved out of the cell and the cell shrank/crenated

Question 20

reflection coefficient of 1 will cause what in the cell?

Answer 20

o those solutes will create a gradient that draws water into the cell.