E1 Chapter 1

Osmoregulation – hormonal control

Case 1: After drinking a large amount of water

Normal water potential in blood

Drinking a lot of water

Increase in water potential in blood

Detected by osmoreceptors

in hypothalamus

Decrease in ADH released by pituitary gland

Decrease permeability of collecting duct to water

Smaller proportion of water is reabsorbed

A large volume of dilute urine produced

Water potential of blood decreases

Negative fe

edback

mechanism

Case 2: After heavy sweating or excessive loss of blood

Normal water potential in blood

e.g heavy sweating

decrease in water potential in blood

Detected by osmoreceptors

in hypothalamus

Increase in ADH released by pituitary gland

Increase permeability of collecting duct to water

Greater proportion of water is reabsorbed

A small volume of concentrated urine produced

Water potential of blood increases

Negative feedback

mechanism

After taking in excess salts Human blood: 0.9% salt concentration normally Maximum salt concentration in urine: 2% Sea water: ~ 3% salt What happens???

[salt]

salt

H2OH2O

Kidney tubule surrounding capillary

A smaller amount of salt & small proportion of water is reabsorbed

A large volume of urine with high salt concentration

Excreted by diffusion & active transport

osmosis