Excretion of dilute urine requires what characteristic of the collecting tubule?

Excretion of dilute urine specifically requires that the collecting tubule be impermeable to water. When the collecting ducts of the nephron are impermeable to water, it prevents water from being reabsorbed back into the bloodstream. As a result, more water remains in the urine, leading to the formation of dilute urine. This physiological process is primarily regulated by the effects of antidiuretic hormone (ADH), which, when present, increases the permeability of the collecting ducts to water, thereby enabling more water reabsorption and the concentration of urine. Conversely, a lack of ADH or a situation where the collecting tubule remains impermeable to water allows for the excretion of water as more dilute urine.

Understanding this mechanism is crucial in grasping how the kidneys regulate fluid balance and electrolyte concentrations within the body.