Roles of hormones in osmoregulation

Question 1

Water potential of blood

Answer 1

• Depends on concentration of solutes and volume of water in the body
• Glucose
• Proteins
• Sodium chloride

Question 2

Rise in concentration of solutes…

Answer 2

• Lowers the water potential = more negative

1. Too little water consumption
2. Too much water
3. Consumption of large amounts of ions

Question 3

Fall in concentration of solutes…

Answer 3

• Increase the water potential = less negative

1. Consumption of large volumes of water
2. Not replacing salts used in metabolism or excreted (not eating enough)

Question 4

Water potential of the blood falls

Answer 4

• Osmoreceptors send nerve impulses to the thirst centre of the brain
• Encouraging the person to drink more

Question 5

ADH

Answer 5

• Increases the permeability of collecting ducts so that more water is reabsorbed into the blood
  = Smaller volume of urine to be produced

Question 6

Diuresis

Answer 6

• Production of large amounts of urine

- ADH has the opposite effect

Question 7

How the body responds to a fall in water potential

Answer 7

• Osmoreceptors in the hypothalamus detect a fall in water potential = water leaves these cells by osmosis
• Osmoreceptors shrink - hypothalamus produces ADH
• ADH passes to posterior pituitary gland - capillaries
• ADH travels in the blood to kidneys - increases permeability to water of cell membrane of cells in walls of DCT and collecting duct

Question 8

How ADH increases the permeability of cell membranes to water (1)

Answer 8

• Specific protein receptors on cell surface membranes bind to ADH molecules
  =enzyme - phosphorylase in the cell
  = Vesicles in cell move out and fuse with cell-surface membrane
• Vesicles contain pieces of plasma membrane that have water channel proteins (aquaporins) = fusion - increase in number of water channels on cell-surface membrane
• Increases permability of membrane to water

Question 9

How ADH increases the permeability of cell membranes to water (2)

Answer 9

• Increases the permeability of collecting duct to urea - passes out
• Further decreasing the water potential of fluid around duct
  = more water leaves the collecting duct by osmosis and re-enters the blood
• Hypothalamus sends less impulses to pituitary gland = release less ADH in blood
• Reverts permeability of cell membranes to original state

Question 10

How the body responds to an increase in water potential

Answer 10

• Osmoreceptors in the hypothalamus detects an increase in water potential
  = less impulses to pituitary glands = reducing the amounts of ADH released
• Decreases permeability of collecting duct to water and urea
• Less water reabsorbed into blood = dilute urine
• Water potential of blood falls to a normal level
• Hypothalamus sends more impulses to pituitary gland
  = increasing amounts of ADH released

Question 11

Negative feedback in osmoregulation

Answer 11

• Decrease in water potential of blood = increase in ADH produced until is it normal level
• Less ADH produced prevents water potential from falling too low
• Increase in water potential of blood = decrease in ADH released until it is normal level
• More ADH produced prevents water potential from increasing too much