The Kidney - Osmoregulation

Detailing how osmoregulation occurs in the collecting duct of the nephron.

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  • Created by: L
  • Created on: 21-01-14 15:38

Osmoregulation

Osmoregulation: the control of water levels and ion levels in the body.

Water is gained from:

  • Food
  • Drink
  • Metabolic processes (e.g. respiration)

-

Water is lost in:

  • Urine
  • Sweat
  • Water vapour when breathing out
  • Faeces
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Adjusting ADH levels in the blood...

  • Water potential of the blood is monitored by osmoreceptors in the hypothalamus.
  • Osmoreceptors respond to the effects of osmosis:
  • When the water potential of the blood is low, water moves out of osmoreceptor calls which causes them to shrink.
  • This stimulates neuroecretory cells in the hypothalamus.
  • These are specialised neurones which produce and release ADH - ADH is produced in the body of these cells (in the hypothalamus) which is then stored in the posterior pituitary gland.
  • When neurosecretory cells are stimulated they send action potentials down their axons, causing the release of ADH, which then enters the blood stream.
  • The target cells of ADH are the cells in the wall of the collecting duct.
  • ADH has a half life of roughly 20 minutes.
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If the blood has a low water potential...

  • This is detected by osmoreceptors in the brain
  • This stimulates the posterior pituitary gland to release more ADH
  • This travels to the kidneys in the bloodstream
  • ADH has the effect of making the collecting duct of the nephron more permiable to water
  • Cells in the wall of the collecting duct have membrane-bound receptors for ADH
  • Aquaporins are placed in the membranes of the cells that line the wall of the collecting duct
  • Water moves out of the collecting duct and into these cells by osmosis, and then from these cells into the bloodstream
  • The overall result is the production of more concentated urine and blood concentration returns to normal levels
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If the blood has a high water potential...

  • Less ADH is produced
  • The plasma membranes of the cells in the wall of the collecting duct fold inwards to remove aquaporins in vesicles
  • This makes the walls less permeable to water
  • Therefore, less water is reabsorbed into the blood by osmosis
  • The urine produced is more dilute
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