| What may cause the lowering of water potential | - Too little water being consumed
- Much sweating occurring
- Large amounts of ions, for example, sodium chloride, being taken in |
| Body response to fall in water potential (1) | - Decrease in water potential of blood e.g. by sweating
- This is detected by osmoreceptors in the hypothalamus
- More ADH released by pituitary glands |
| Body response to fall in water potential (2) | - Increases permeability of collecting duct to water by increasing no. of aquaporins
- More h2o leaves collecting duct by osmosis
- Increase in water potential of blood |
| Body response to fall in water potential (3) | - When the water potential is returned to normal, osmoreceptors cause pituitary to release less ADH (=negative feedback) |
| Body response to rise in water potential (1) | - The osmoreceptors in the hypothalamus detect the rise in water potential + increase frequency if nerve impulses to the pituitary gland to reduce its release of ADH |
| What may cause the rise of water potential (2) | - Less ADH, via the blood, leads to a decrease in the permeability of the collecting ducts of water + urea
- Less water is reabsorbed into the blood from the collecting duct |
| What may cause the rise of water potential (3) | - More dilute urine is produced
- Water potential of blood falls |
| What may cause the rise of water potential (4) | - When the water potential of the blood has returned to normal, the osmoreceptors in the hypothalamus cause the pituitary to raise its ADH release back to normal levels (=negative feedback) |
