1. Osmoregulation – hormonal control
E1 Chapter 1
Osmoregulation – hormonal control

2. Case 1: After drinking a large amount of water
Decrease permeability of collecting duct to water
Decrease in ADH released by pituitary gland
Detected by osmoreceptors in hypothalamus
Negative feedback mechanism
Smaller proportion of water is reabsorbed
Increase in water potential in blood
Drinking a lot of water
Water potential of blood decreases
A large volume of dilute urine produced
Normal water potential in blood

3. Case 2: After heavy sweating or excessive loss of blood
A small volume of concentrated urine produced
Normal water potential in blood
Water potential of blood increases
e.g heavy sweating
Negative feedback mechanism
Greater proportion of water is reabsorbed
decrease in water potential in blood
Increase permeability of collecting duct to water
Increase in ADH released by pituitary gland
Detected by osmoreceptors in hypothalamus

4. After taking in excess salts
Human blood: 0.9% salt concentration normally
Maximum salt concentration in urine: 2%
Sea water: ~ 3% salt
What happens???
Excreted by diffusion & active transport
A smaller amount of salt & small proportion of water is reabsorbed
A large volume of urine with high salt concentration
[salt]
salt 
osmosis
H2O
H2O
Kidney tubule surrounding capillary