Manitoba Nephrology Nurse Practice Test

The action of antidiuretic hormone (ADH), also known as vasopressin, in the collecting duct is crucial for regulating the body's water balance. When ADH is present, it binds to the receptors in the cells of the collecting duct, which triggers a series of events leading to the insertion of aquaporin channels into the apical membrane of these cells. Aquaporins are specialized water channels that allow water to be reabsorbed from the filtrate back into the bloodstream. As a result, the reabsorption of water increases, which concentrates the urine and reduces water loss from the body. This mechanism is especially important for maintaining homeostasis and ensuring that the body retains sufficient water when hydration levels are low. In conditions of dehydration or elevated plasma osmolality, ADH secretion increases, enhancing this effect. Therefore, the correct understanding of ADH’s role in the collecting duct is that it significantly increases the reabsorption of water.