Osmoregulation
Osmoregulation
- Osmoregulation controls the water content of the blood.
- It is run by the brain, using a hormone called ADH.
- It is a clear example of negative feedback.
The ADH pathway
- The hypothalamus detects the water potential of the blood.
- When the blood is too concentrated, the pituitary gland releases antidiuretic hormone (ADH).
- ADH makes the collecting ducts more permeable to water by adding water channels (aquaporins).
- More water is reabsorbed into the blood, so less, more concentrated urine is made.
Practice
Which part of the brain detects the water potential of the blood?
The hypothalamus monitors blood water potential and triggers ADH release from the pituitary.
Practice
ADH increases water reabsorption by:
ADH inserts aquaporins into the collecting duct membranes, so more water is reabsorbed.
Practice
When the blood is too concentrated, the body:
More ADH means more water returned to the blood, restoring its water content (negative feedback).
Negative feedback in action
- Too concentrated → more ADH → more water reabsorbed → blood water restored.
- Too dilute → less ADH → less water reabsorbed → more dilute urine.
- Either way, the change is corrected — negative feedback.
Practice
Osmoregulation by ADH is an example of negative feedback.
A change in blood water triggers a response that returns it to normal — classic negative feedback.
You've got it
Key idea
- osmoregulation controls blood water content
- the hypothalamus detects water potential; the pituitary releases ADH
- ADH adds aquaporins to the collecting ducts → more water reabsorbed → concentrated urine
- it works by negative feedback (more ADH when blood is too concentrated)