Question

What happens to the walls of distal convoluted tubule (DCT) of a nephron when vasopressin is released by the pituitary into the stream?

Answer 1

Where there is an increase in osmolality of the plasma, ADH release is increased. The increase in ADH release will mean that the permeability of the DCT cells to water increases and urine output decreases. ADH increases the transcription and insertion of Aquaporin–2 channels to the apical membrane of the DCT. This allows water to move down its concentration gradient, out of the nephron and back into the bloodstream. This increases the water reabsorbed from the urine, in order to decrease plasma osmolality and increase total blood volume. Water reabsorption in this manner is a passive process.

Alternatively, when there is a decrease in osmolality of the plasma then ADH release is inhibited. This results in a decrease in the number of Aquaporin-2 channels being inserted into the apical membrane of the DCT. Therefore there is a reduction in the amount of water reabsorbed from the nephron back in the bloodstream.