Physiologically, ADH is produced at the hypothalamus and stored in the posterior pituitary gland. Under physiological conditions, hyponatraemia and low osmolality inhibit the excretion of urinary sodium by stimulating the secretion of ADH. ADH acts on the renal distal tubules and enhances the reabsorption of water, so serum osmolality is maintained at the normal level; urinary sodium concentration and osmolality decrease (urinary sodium concentration below 10mmol/l).
