Lecture 4

Question 1

Explain water transport?

Answer 1

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

Question 2

What is the definition of concentration?

Answer 2

the mass of a substance in a known volume

Question 3

How does water move?

Answer 3

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.

Question 4

What are the two driving forces of water movement?

Answer 4

1. Osmotic force- water wanting to move to an area of high solute
2. Hydrostatic driving forces- the effect of gravity on the fluid across capillary endothelial cells

Question 5

What is the van’t Hoff equation?

Answer 5

This equation is used to calculate the osmotic pressure of a solution.

pie = nRTC

Question 6

What is water flux and what is the equation?

Answer 6

A difference in osmotic pressure between two compartments that leads to water movement

Jv = Kh A [RC (Ci - Co)]

Question 7

Describe osmosis?

Answer 7

The flow of water between two solutions that are separated by a semi-permeable membrane

water will flow from low osmolarity to high osmolarity

Question 8

What does the reflection coefficient (RC) represent?

Answer 8

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.

Question 9

How is osmolarity different from tonicity?

Answer 9

Osmolarity is the total concentration of all particles in the solution

on the other hand, tonicity is only the concentration of active particles.

Question 10

What kind of particles contribute to tonicity?

Answer 10

ONLY impermeable particles will contribute to the tonicity and cause changes in cell volume

Question 11

What describes the volume change of a cell at equilibrium?

Answer 11

tonicity

Net water movement will be into the compartment that has the higher concentration of non-penetrating solutes.

Question 12

What kinds of solutes can penetrate the membrane?

Answer 12

glucose, urea, and glycerol

solutes will distribute to equilibrium

Question 13

What kinds of solutes cannot penetrate the membrane ?

Answer 13

sucrose, NaCl, KCl

water will move in to dilute solutes

these solutes determine tonicity!!!

Question 14

Explain iso-osmotic, hyperosmotic, and hypo-osmotic?

Answer 14

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

Question 15

Explain isotonic, hypertonic, and hypotonic?

Answer 15

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

Question 16

150 mM of NaCl + 50 mM of glycerol

osmolarity? tonicity? water movement?

Answer 16

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)

Question 17

170 mM NaCl + 10mM glycerol

osmolarity? tonicity? water movement?

Answer 17

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!

Question 18

75 NaCl + 10 mM glycerol

osmolarity? tonicity? water movement?

Answer 18

75 x 2 =150 + 10 x 1 =160

hypo-osmotic!!!

150 (NaCl) = hypotonic!

Water will enter cell

Question 19

All hypo-osmotic solutions are?

Answer 19

hypotonic

Question 20

iso-osmotic solutions can be?

Answer 20

hypotonic or isotonic

Question 21

hyperosmotic solutions can be?

Answer 21

hypo, hyper, or isotonic

Question 22

5 percent dextrose in water

Answer 22

isotonic, but physiologically hypotonic

Question 23

10 percent dextrose in water

Answer 23

hypertonic

Question 24

0.45 percent saline

Answer 24

hypotonic

Question 25

0.9 percent saline

Answer 25

isotonic

Question 26

3.0 percent saline

Answer 26

hypertonic

Question 27

why use 5 percent dextrose in water?

Answer 27

Used to replace water loss and treat hypernatremia

170 cal and no electrolytes

Question 28

why use 10 percent dextrose in water?

Answer 28

provides free water

340 cal and no electrolytes

Question 29

why use 0.45 percent saline?

Answer 29

provides free water in addition to Na and Cl
used to replace hypotonic fluid loss

no cals

Question 30

why use 0.90 percent saline?

Answer 30

Used to expand intravascular volume and replace extracellular fluid loss

does not provide free water

may cause intravascular overload and hyperchloremic acidosis

Question 31

why use 3.0 percent saline?

Answer 31

Used to treat symptoms of hyponatremia

must be given slowly and with caution because it could lead to intravascular fluid overload and pulmonary edema