PHYS Y1 S1: Body Fluids

Question 1

diffusion

Answer 1

• net movement of small & uncharged particles from high conc to low conc until equilibrium is reached (passive)

Question 2

facilitated diffusion

Answer 2

• net movement of large & charged particles from high conc to low conc via a protein channel until equilibrium is reached (passive)

Question 3

active transport

Answer 3

• net movement of particles from low conc to high conc via a protein pump (active)

Question 4

5 factors affecting the rate of diffusion

Answer 4

• temp
• conc grad
• molecule size
• surface area
• membrane permeability (no. of protein pumps/channels)

Question 5

osmosis

Answer 5

• net movement of water particles from high conc to low conc

Question 6

osmotic pressure

Answer 6

• amt of force required to counteract the movement of water across a membrane

Question 7

osmolarity

Answer 7

• concentration of ALL dissolved particles
• e.g. 1 mol glucose/L = 1 osmole/L because it doesn’t dissociate when dissolving
• e.g. 1 mol NaCl/L = 2 osmoles/L because it dissociates into 2 ions - Na+ and Cl- when dissolving

Question 8

tonicity

Answer 8

• concentration of NON-DIFFUSIBLES e.g. glucose, ions (EFFECTIVE OSMOLES)
• ultimate fate of water movement

Question 9

how to work out where water will move

Answer 9

1. work out where DIFFUSIBLE particles will go to reach equilibrium
2. water will follow
   (don’t consider non-diffusibles)

Question 10

can water cross the plasma membrane?

Answer 10

• technically yes but this is negligible so aquaporins are needed

Question 11

what happens when 0.9% NaCl is injected intravenously?

Answer 11

• cells will neither swell nor shrink (stay same)
• because 0.9% NaCl is isotonic and iso-osmolar to ICF

Question 12

why is pure water never given IV

Answer 12

too hypotonic so moves into cells and causes them to lyse

Question 13

what is volume depletion and how to treat

Answer 13

• loss of water and ions in ECF (dehydrated)
• give 0.9% NaCl because it’s isotonic so no net movement of water into cell, but water and ions will still be replenished in ECF

Question 14

what is water depletion and how to treat

Answer 14

• loss of water in ICF
• give 5% glucose because isotonic so not much happens with glucose but the water will move into cells (if hypoglycaemic you would use higher conc of glucose)

Question 15

identify tonicity and osmolarity of 1.8% urea and describe its effect on cells

Answer 15

• hypotonic and iso-osmolar compared to ICF
• urea diffuses into cell > water follows > lysis
• urea never given IV b/c causes lysis

Question 16

identify tonicity and osmolarity of 5% glucose and describe its effect on cells

Answer 16

• isotonic and iso-osmolar > later becomes hypotonic
• once glucose is metabolised in the cell, its concentration in ICF will decrease
• then glucose will diffuse in from ECF
• water will move into cells (don’t lyse b/c occurs slowly)
• both ECF and ICF will increase in volume

Question 17

osmolarity of RBC ICF

Answer 17

300 mOsm/L

Question 18

ratio of ICF and ECF

Answer 18

• 2/3 ICF
• 1/3 ECF

Question 19

why does urea make water move even tho it is a non-diffusible?

Answer 19

• whenever something moves across the membrane, water will follow. this is NOT osmotic pressure.
• compared with Na+/Cl-, they can’t move across the membrane and therefore generate osmotic pressure depending on conc grad

Question 20

how does glucose move across the membrane?

Answer 20

• if its from the bloodstream into RBC, then it’s facilitated uniport diffusion
• in contexts such as the small intestine or kidneys, it will be active transport