Osmoregulation refers to the regulation and maintenance of blood volume, body fluid volume, and ionic concentration in the body. Osmoreceptors in the body are activated by changes in these parameters. When there is excessive fluid loss, these receptors stimulate the hypothalamus to release antidiuretic hormone (ADH) or vasopressin, which facilitates water reabsorption from the tubules to prevent diuresis. The counter current mechanism in the Henle's loop and vasa recta helps maintain an osmolarity gradient from 300 mOsmol/L in the cortex to about 1200 mOsmol/L in the inner medulla. The collecting duct also contributes by maintaining pH and ionic balance of blood through selective secretion of H⁺ and K⁺ ions.