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:
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- 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
