16.7 hormones in osmoregulation

Question 1

Fall in water potential

Answer 1

1. osmoreceptors in hypothalamus detect fall by water being lost from them via osmosis
2. shrinking cells cause ADH to be produced
3. ADH passes to posterior pituitary gland and is secreted into capillaries
4. ADH passes in blood to kidney
5. specific protein receptors on csm binds to ADH, leading to activation of enzyme phosphorylase in cell
6. activated phosphorylase causes cell vesicles to move and fuse with csm
7. vesicles contain pieces of plasma membrane with water channel protiens so when fused, aquaporins are increases making csm more permeable
8. ADH increases permeability of collecting duct to urea so it movesout, furthering lower wpt of fluid around duct
9. water leaves collecting duct by osmosis down wpt gradient and re-enters blood
10. only maintains wpt of blood, not increasing
11. nerve impulses sent to thirst centre of brain

Question 2

ADH

Answer 2

antidiuretic hormone

Question 3

negative feedback

Answer 3

1. osmoreceptors in hypothalamus detect rise/fall
2. send fewer impulses to pituitary gland
3. reduces/increases release of ADH
4. permeability of collecting ducts to water and urea reverts

Question 4

causes of rise in wpt

Answer 4

1. large volume of water being consumes
2. salts used in metabolism or excreted not being replaced in diet

Question 5

causes of fall in wpt

Answer 5

1. too little water being consumes
2. much sweating
3. large amounts of ions being taken in e.g. NaCl

Question 6

rise in wpt

Answer 6

1. osmoreceptors in hypothalamus detect rise
2. increase nerve impulses to pituitary gland to reduce release ADH
3. less ADH via blood decreases permeability of collecting ducts to water and urea
4. less water reabsorbed into blood from collecting duct
5. more dilute urine produced and wpt blood falls