Juxtamedullary nephrons have a longer loop of Henle that cortical nephrons and as we know this loop has a great function reabsorving water, the longer it is more water is reabsorved. The descending portion of the loop is permeable to ions but not to water so this portion reaborves a great quantity of water. Then in the ascending loop is the opposite, it is permeable to water but not to ions. The ions reabsorved in the ascending loop (20-25% of the Na+) are responsable of the water reabsorved in the descending loop. The longer the loop is more water and ions are reabsorved.
