ADH and water level

Homeostasis and response · Hormonal coordination in humans · note 6 of 11

Spec 4.5.3.3Triple onlyHigher tierDownload these notes (PDF)12 pages

ADH and water levelSpec 4.5.3.3

The water level in the body is controlled by the hormone ADH, which acts on the kidney tubules. ADH is released by the pituitary gland when the blood is too concentrated. It causes more water to be reabsorbed back into the blood from the kidney tubules. It does this by making the kidney tubules more permeable to water.

	Blood too concentrated (not enough water)	Blood too dilute (too much water)
ADH released by pituitary	More	Less
Permeability of kidney tubules to water	Increases	Decreases
Water reabsorbed into the blood	More	Less
Urine	Small volume, concentrated	Large volume, dilute

This is controlled by negative feedback: when the water level returns to normal, less ADH is released.

Negative feedback loop for water: blood too concentrated, pituitary gland releases more ADH, kidney tubules become more permeable to water, more water is reabsorbed into the blood, blood becomes more dilute, and less ADH is released. — ADH makes the kidney tubules more permeable to water. As the blood returns to normal, less ADH is released.