Why are sodium and water only partly reabsorbed (in the PCT)?Watch
My answer is this: Sodium and water are reabsorbed iso-osmotically in the the PCT i.e the absorption is driven by the active transport of Na+ out of the filtrate into the surrounding capillaries followed by water because of osmosis (since the fluid in PCT would have a higher water potential after Na+ is absorbed back). However water cannot be completely reabsorbed since it is required for the removal of urea. Therefore Na+ is only partly reabsorbed to allow water to not be fully absorbed since it is needed for the removal of urea. The distal convoluted tubule then fine tunes the amount of sodium eliminated depending on the actual sodium ion concentration in the blood.
Is this correct?