- n example of negative feedback
- 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
- This is controlled by the hormone ADH
- 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 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 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
The kidney controls water levels using the hormone ADH. It is an example of a negative feedback mechanism.
Remember the negative feedback cycle covered in 7.2.1: the brain detects if the level is too high or low and modulates how much ADH the pituitary gland releases