Water Movement Membrane

Question 1

How does water move across membrane?

Answer 1

Can move readily across hydrophobic membrane as its small and uncharged
Diffusion driven by osmotic gradient of solutes

Question 2

Distribution of water in the body

Answer 2

42 L in 70kg man
1/3 - extracellular —> 10.5L interstitial fluid, 3.5L plasma
2/3 - intracellular

3.5L plasma + 2L blood = 5.5L blood

Question 3

How are ions distributed in cell?

Answer 3

Higher outside:
Na+ (145mM, 12mM)
Cl- (123mM, 4.2mM)
Ca2+ (1.5mM, 10^-7mM)

Higher inside:
K+ (140mM, 4mM)

Question 4

Tonicity of solution

Answer 4

Isotonic - equal solute and water
Hypotonic - more water, less solute
Hypertonic - more solute, less water

Water moves:
Hypotonic —> Isotonic —> Hypertonic

Question 5

What happens to cells in hypotonic solution

Answer 5

Swell and burst (lysis)

Question 6

What happens to cells in hypertonic solution?

Answer 6

Lose water, shrivel and lyse

Question 7

Osmolality

Answer 7

Osmoles per kilogram of water

1 mole Glucose forms 1 Osmolar solution in 1L water
1 mole of NaCl forms 2 osmolar solution in 1L water
1 mole of CaCl2 forms 3 osmolar solution in 1L of water

1osmole/kg = 1 osmole/L

Question 8

Osmotic pressure

Answer 8

The pressure required to stop the flow of water to equalise hyperosmotic solution

Question 9

What are aquaporins

Answer 9

Integral proteins
13 isoforms - important and specific roles
Channels for water - permit rapid diffusion above rate of passive

Question 10

How does water move through aquaporins?

Answer 10

Depends on solute concentration
Hydrophilic pore with positive residues (repels H+ and other ions so does not disrupt)
Single file passage