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
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