REGULATION OF BLOOD WATER POTENTIAL

• WHAT CAUSES A DECREASE IN WATER POTENTIAL?

  • too little water consumed
  • much sweating
  • large ion intake
• RESPONSE TO DECREASE IN WATER POTENTIAL?

  1. Osmoreceptors in hypothalamus detect
  2. Water lost from cells by osmosis, shrink
  3. Hypothalamus produces ADH
  4. Passes to posterior PG and capillaries via blood to kidney
  5. Increase permeability of cells making up DCT and CD walls
  6. Specific protein receptors on CSM bind to ADH
  7. Activate phosphorylase
  8. Vesicles fuse with CSM
  9. Contain aquaporins, increasing number of water channels and permeability
  10. CD permeability to urea increases
  11. Urea moves out and lowers water potential of fluid around CD
  12. Water leaves CD, lowers water potential and re-enters blood
• WHAT HAPPENS WHEN WATER RE-ENTERS THE BLOOD?

  • does not increase water potential of blood, only stops it from decreasing further
  • nerve impulses sent to thirst centre of brain
  • osmoreceptors detect rise in water
  • send fewer impulses to pituitary gland
  • reduce release of ADH
  • permeability returns to normal
• WHAT IS OSMOREGULATION AN EXAMPLE OF?

  negative feedback
• WHY DOES BLOOD WATER POTENTIAL INCREASE?

  • large volumes of water being consumed in diet
  • salt in metabolism/ excreted not replaced in diet
• RESPONSE TO INCREASE IN WATER POTENTIAL?

  1. Osmoreceptors in hypothalamus detect increase
  2. Increase frequency of nerve impulses to pituitary gland to reduce ADH release
  3. Decreases permeability of collecting duct to water/ urea
  4. Less water reabsorbed into blood from collecting duct
  5. More dilute urine produced
  6. Water potential of blood decreases
  7. Once returned to normal, osmoreceptors cause pituitary gland to raise ADH back to normal levels
• WHAT DOES ADH STAND FOR?

  anti-diuretic hormone