What effect does antidiuretic hormone (ADH) have on the collecting ducts?

Antidiuretic hormone (ADH), also known as vasopressin, plays a crucial role in regulating water balance in the body by acting on the collecting ducts of the kidneys. When ADH is released, it promotes the insertion of water channels, specifically aquaporins, into the membranes of collecting duct cells. This process increases the permeability of these ducts to water.

As a result, when ADH is present, the collecting ducts can reabsorb more water from the filtrate back into the bloodstream, leading to concentrated urine and reduced urine output. This mechanism is essential for the body’s ability to conserve water, especially during times of dehydration or when blood osmolarity is high.

The other options do not accurately describe the primary action of ADH on the collecting ducts. For instance, while potassium regulation occurs in the nephron, it is distinctly separate from the direct action of ADH, which focuses specifically on water permeability. Similarly, the absorption of ions is not the primary function of ADH in this context. Thus, the correct choice highlights the essential role of ADH in increasing water reabsorption, which is pivotal for maintaining homeostasis in body fluid levels.