ADH in Water Reabsorption (OCR GCSE Biology A (Gateway))

The Role of Anti-Diuretic Hormone (ADH)

Higher Tier Only

• Water reabsorption occurs along the nephron tubules in the kidneys

• The control of water reabsorption by the tubules is an example of negative feedback

• This is controlled by the hormone ADH 

  • If the water content of the blood is too high then less water is reabsorbed, if it is too low then more water is reabsorbed

  • The pituitary gland in the brain constantly releases ADH

    • How much ADH is released depends on how much water the kidneys need to reabsorb from the filtrate

  • ADH affects the permeability of the tubules to water

• If the water content of the blood is too low:

  • The pituitary gland releases more ADH which leads to more water being reabsorbed in the tubules of the kidney (the tubules become more permeable to water)

  • As a result, the kidneys produce a small volume of concentrated urine

If blood water content is low, more ADH is released, increasing permeability of the tubules, so more water is reabsorbed from the urine

• If the water content of the blood is too high:

  • The pituitary gland releases less ADH which leads to less water being reabsorbed in the tubules of the kidney (the tubules become less permeable to water)

  • As a result, the kidneys produce a large volume of dilute urine

If blood water content is high, less ADH is released so more water is lost in the urine