When there is excessive water loss from the body due to
increased sweating, excessive vomitting or diuresis, the plasma
osmolarity increases and blood fluid volume is decreased.
Increased plasma osmolarity is detected by osmoreceptors in
hypothalamus.
Hypothalamus intiates two responses :
- Increase in thirst
- Release of ADH
Increased thirst will lead to increased water intake.
Anti-diuretic hormone released from posterior pituitary gland will
increase water reabsorption at collecting duct of nephron to
prevent diuresis.
Due to high water intake and decreased water loss, the fluid
volume in the body increases back to normal.