The loss of water from the descending limb multiplies the concentration that can be achieved at each level of the loop through the active extrusion of Na+ (with Cl– following passively) by the...

The loss of water from the descending limb multiplies the concentration that can be achieved at each level of the loop through the active extrusion of Na+ (with Cl– following passively) by the ascending limb. The longer the loop of Henle, the longer the region of interaction between the descending and ascending limbs, and the greater the total concentration that can be achieved. In a human kidney, the concentration of fi ltrate entering the loop is 300 milliosmolar (mOsm), and this concentration is multiplied to more than 1200 mOsm at the bottom of the longest loops of Henle in the renal medulla.