Final answer:
Vasopressin, or antidiuretic hormone (ADH), promotes the reabsorption of water in the kidneys by increasing the permeability of the distal convoluted tubule and collecting ducts to water through the insertion of aquaporin channels.
Step-by-step explanation:
The action promoted by vasopressin, also known as antidiuretic hormone (ADH), is reabsorption of water from the urine back into the bloodstream. ADH acts on the distal convoluted tubule (DCT) and the collecting ducts of the kidney nephrons. By stimulating the insertion of aquaporin water channels into the cell membranes of the kidney tubules, it allows water molecules to pass through and be reabsorbed by osmosis into the peritubular capillaries, thus conserving water and regulating the body's fluid balance. Approximately 90% of water is reabsorbed prior to reaching the collecting ducts where ADH has its effect, influencing the final 10% of water recovery. This hormone plays a crucial role in maintaining blood volume and pressure.