osmoregulation

Question 1

what does ADH do

Answer 1

it increases the permeability of the collecting duct by opening aquaporins

• makes cells lining collecting duct more permeable to water
• binds to receptors - vesicles with aquaporins on membrane fuse with cell-surface membrane

Question 2

what does the loop of henle do

Answer 2

creates a salty high Na+ conc region in the medulla

• counter current multiplier system

ascending limb pumps out Na+
descending limb loses H2O by osmosis and absorbs Na+ by diffusion so filtrate gets more concentrated

as liquid passes by the ascending limb its concentration drops because Na+ pumped out by H2O cannot follow by osmosis because the ascending limb is impermeable

salty region creates osmotic pull on the filtrate in the collecting duct

Question 3

ADH levels

Answer 3

high - collecting duct very permeable to H2O - a lot of H2O drawn out by osmosis - small volume of urine

low - collecting duct not permeable - no H2O drawn out - large volume

Question 4

what are the receptors and where are they

Answer 4

osmoreceptors in hypothalamus - detect blood water potential

posterior pituitary gland sends out ADH into blood stream

Question 5

the osmoregulation in steps

Answer 5

1. drink a lot
2. water potential increases above restricted limits
3. high blood water potential detected by osmoreceptors in the walls of blood vessels in hypothalamus
4. send a nervous signal to posterior pituitary gland
5. reduce ADH secretion
6. kidney - collecting duct less permable
7. less H2O drawn out into high Na+ conc region
8. higher volume, more dilute urine produced
9. water potential decreases