15.6 The Kidney & Osmoregulation

Question 1

What is osmoregulation?

Answer 1

Balance & control

of blood water potential

Question 2

What does ADH control?

Answer 2

PERMEABILITY of collecting duct walls 
  ￬
volume of water reabsorbed 
  ￬
volume & concentration of urine

Question 3

What are examples of water gains?

Answer 3

Drinking Food Aerobic respiration

Question 4

Explain how aerobic respiration is an example of water gain using a word equation:

Answer 4

Oxygen + Glucose ⟶ WATER + Carbon dioxide

Water is a product of aerobic respiration,

therefore increases volume of water in the body.

Question 5

What are examples of water losses?

Answer 5

Urine Sweat Exhalation Faeces

Question 6

Outline the mechanism of ADH action:

Answer 6

1. ADH SECRETED by posterior PITUITARY GLAND in hypothalamus ⟶ BLOODSTREAM.
   - carried to cells of collecting duct.
2. ADH BINDS to RECEPTORS on plasma membrane of collecting duct cells.
   - Triggers formation of secondary messenger, cAMP
   - cAMP causes cascade of events:
3. In tubule cells, VESICLES FUSE with plasma membrane.
4. These vesicles contain AQUAPORINS&raquo_space; inserted into plasma membrane.
   
   • Aquaporins INCREASE PERMEABILITY of plasma membrane to water.
5. Water moves OUT of tubule cells ⟶ tissue fluid ⟶ VASA RECTA, by OSMOSIS

Question 7

What is a secondary messenger?

Answer 7

molecule which relays signal received at plasma membrane of cell

to molecules inside cell.

e.g cAMP during osmoregulation

Question 8

Explain the effect of increasing ADH on the volume of water reabsorbed:

Answer 8

higher concentration ADH

= more VESICLES formed

= more AQUAPORINS inserted into plasma membrane

= greater membrane PERMEABILITY to water

= higher VOLUME water REABSORBED

Question 9

What is the stimulus that osmoreceptors detect during osmoregulation?

Answer 9

change in concentration of INORGANIC IONS in blood.

which are an indicator of blood water potential, and therefore indicate concentration of water in the blood

Question 10

Outline the negative feedback process when water is in SHORT SUPPLY:

Answer 10

• Short supply of water = high CONCENTRATION of INORGANIC IONS in blood
◦ low water potential

• Detected by OSMORECEPTORS in hypothalamus

1. Sends NERVE IMPULSES to posterior PITUITARY GLAND
2. ADH secreted ⟶ bloodstream
3. BINDS to RECEPTORS on tubule cells&raquo_space; increased PERMEABILITY of collecting duct
4. MORE water REABSORBED into vasa recta

• SMALL VOLUME of CONCENTRATED urine produced

Question 11

Outline the negative feedback process when water is in EXCESS:

Answer 11

• Excess water = low CONCENTRATION of INORGANIC IONS in blood
◦ high water potential

• Detected by OSMORECEPTORS in hypothalamus

1. INHIBITS NERVE IMPULSES to posterior PITUITARY GLAND
2. little/no ADH secreted ⟶ bloodstream
3. less/no ADH binds to RECEPTORS on tubule cells&raquo_space; low PERMEABILITY of collecting duct
4. little/no water REABSORBED into vasa recta

• LARGE VOLUME of DILUTE urine produced

Question 12

What is an aquaporin?

Answer 12

Type of CHANNEL protein,

specialised to TRANSPORT WATER MOLECULES

in/out of cells.

Question 13

What is ADH?

Answer 13

Anti-diuretic hormone

Involved in increasing permeability of collecting duct walls for reabsorption during osmoregulation.

Question 14

What symptoms would be seen if a person did not produce sufficient ADH?

Answer 14

• Constantly producing large volumes of dilute urine regardless of water intake
• Dehydration
• Crenation of cells