Define Antidiuretic Hormone - Posterior Pituitary

Antidiuretic hormone or ADH, also known as vasopressin, is another polypeptide containing 9 amino acids. As the name of the hormone suggests, its major action is to prevent diuresis i.e., it reduces the rate of urine formation. This hormone acts on the distal tubules of the kidney controlling the reabsorption of water.

When the osmotic pressure is high, the osmoreceptors respond by stimulating the secretion of antidiuretic hormone which increases the reabsorption of water by the renal tubules. ADH is often called vasopressin because under the influence of this hormone, the smooth muscles of the intestine and blood vessels contract. Contraction of the muscle layer in the blood vessel wall increases the blood pressure. Hence the name vasopressin. Hence, in dehydrated or malabsorptive diseases, these hormones try to regulate the water and mineral balance of the body by adjusting the quantity of urine formation in the kidney.