5.2.7 osmoregulation

Question 1

antidiuretic hormone (ADH)

Answer 1

hormone which control permeability of collecting duct walls

Question 2

osmoreceptor

Answer 2

sensory receptor that detects changes in water potential

Question 3

osmoregulation

Answer 3

control of water potential in body (includes salts too)

Question 4

3 sources of water

Answer 4

• food
• drink
• metabolism (eg. respiration)

Question 5

4 ways water is lost from the body

Answer 5

• urine
• sweat
• water vapour in exhaled air
• faeces

Question 6

what do the kidneys act as

Answer 6

effector to control water content of body & salt concentration in body fluids

Question 7

mechanism of osmoregulation: conserving less water (cool day/hydrated)

Answer 7

• walls of collecting duct become less permeable
• less water reabsorbed
• greater volume of urine produced

Question 8

mechanism of osmoregulation: conserve more water (hot day/dehydrated)

Answer 8

• collecting duct walls made more permeable
• more water reabsorbed into blood
• produce smaller volume of urine

Question 9

what do the cells in the walls of the collecting duct have

Answer 9

membrane-bound receptors for ADH

Question 10

effect of ADH on membrane-bound receptors in cell walls of collecting duct

Answer 10

• ADH binds to receptors & causes chain of enzyme-controlled reactions inside cell
• end result = cause vesicles containing water-permeable channels (aquaporins) to fuse will cell surface membrane
• makes walls more permeable

Question 11

aquaporins

Answer 11

water-permeable channels

Question 12

what happens when levels of ADH in blood rises

Answer 12

• more water-permeable channels inserted
• allows more water to be reabsorbed by osmosis (into blood)
• less urine produced & has lower water potential

Question 13

what happens when levels of ADH in blood falls

Answer 13

• cell surface membrane folds inward (invaginates) = creates new vesicles to remove water-permeable channels from membrane
• makes walls less permeable & less water reabsorbed by osmosis (into blood)
• more water passes down collecting duct = greater volume of urine which is more dilute (higher water potential)

Question 14

summary of effect of ADH on wall of collecting duct

Answer 14

1. ADH detected by cell surface receptors
2. chain of enzyme-controlled reactions
3. vesicles containing aquaporins fuse to membrane
4. more water reabsorbed

Question 15

what does the hypothalamus in the brain contain

Answer 15

specialised cells = osmoreceptors

Question 16

what do osmoreceptors respond to & how

Answer 16

effects of osmosis
- water potential in blood low (negative) = osmoreceptor cell loses water by osmosis & shrinks
- stimulate neurosecretory cells in hypothalamus

Question 17

neurosecretory cells
- what are they
- how do they produce ADH

Answer 17

= specialised neurones which produce/release ADH

• ADH manufactured in cell body (lies in hypothalamus)
• ADH moves down axon to terminal bulb in posterior pituitary gland
• stored in vesicles
• when stimulated by osmoreceptors = carry action potential down axons & cause release of ADH by exocytosis

Question 18

what is osmoregulation an example of

Answer 18

negative feedback

Question 19

negative feedback: increase of water potential in blood

Answer 19

1. detected by osmoreceptors in hypothalamus
2. less ADH released from posterior pituitary gland
3. collecting duct walls less permeable
4. less water reabsorbed into blood & more urine produced
   = decrease in water potential of blood

Question 20

negative feedback: decrease of water potential in blood

Answer 20

1. detected by osmoreceptors in hypothalamus
2. more ADH released from posterior pituitary gland
3. collecting duct walls more permeable
4. more water reabsorbed & less urine produced
   = increase in water potential of blood

Question 21

how is ADH transported from the posterior pituitary gland to the collecting duct

Answer 21

• ADH enters blood capillaries running through posterior pituitary gland
• transported around bound & acts on cells of collecting ducts