Final answer:
ADH increases the permeability of the collecting ducts in the kidneys to water by causing aquaporin water channels to move to the cell membrane, resulting in increased water reabsorption and more concentrated urine when hydration levels are low.
Step-by-step explanation:
The antidiuretic hormone (ADH) plays a crucial role in regulating the water balance within the body by altering water permeability in the kidneys. When ADH is secreted, it induces the movement of aquaporin water channels to the plasma membrane of cells in the collecting ducts.
This results in an increase in water reabsorption, as water moves through these aquaporins back into the bloodstream, leading to a more concentrated urine if body hydration is low.
If the body is well-hydrated, resulting in a decrease in ADH levels, aquaporins are removed from the apical membrane of the principal cells, reducing water permeability and thus producing more dilute urine.
The presence or absence of aquaporins in the collecting ducts is a crucial factor in the process of urine concentration, and it directly affects the regulation of blood osmolarity, blood pressure, and urine osmolarity.