1. Osmoreceptors detect a reduction in the water potential of the blood and they produce ADH.
2. ADH is transported to the posterior pituitary gland and secreted into the bloodstream.
3. The blood transports ADH to the kidneys.
4. ADH binds to receptor proteins on the cells lining the distal convoluted tubule and collecting duct.
5. This stimulates the second messenger cyclic AMP (cAMP), which activates a cascade leading to the phosphorylation and integration of aquaporin molecules into the cell-surface membrane.
6. This increases the permeability of the cells to water.
7. More water is reabsorbed from filtrate into the blood.
8. A smaller volume of more concentrated urine is produced.

Osmoregulation is the homeostatic control of the water potential of the blood.

1. Not consuming enough water
2. Excessive sweating
3. Intake of large amounts of ions, such as by eating salty food

A reduction in water potential coincides with a rise in solute concentration.

The cells that detect a decrease in water potential are called osmoreceptors.

Osmoreceptors are located in the hypothalamus of the brain.

They are specifically found in the walls of blood vessels in the hypothalamus.

Water moves from osmoreceptor cells into the blood by osmosis. This causes osmoreceptors to shrink and produce antidiuretic hormone (ADH).

The posterior pituitary gland stores ADH that has been produced by osmoreceptors in the hypothalamus.

When stimulated, the posterior pituitary gland secretes ADH into capillaries so it can be transported to the kidneys.

Aquaporins are water channel proteins that can embed in the cell surface membrane of cells in the distal convoluted tubule and the collecting duct.

1. The osmoreceptors in the hypothalamus detect the increased water potential in the blood.
2. The osmoreceptors send fewer impulses to the pituitary gland, reducing the release of ADH.
3. This leads to a decrease in the permeability of the collecting ducts to water.
4. Less water is reabsorbed into the blood.
5. A larger volume of more dilute urine is produced.

Antidiuretic hormone (ADH) makes the distal convoluted tubule and the collecting duct more permeable to water and urea, allowing more water to be reabsorbed from filtrate into the blood.