It uses this system in which the filter travels downward here, but upward here, to multiply to increase the amount of water that is reabsorbed back by our body from the filtrate. At the same time, it concentrates the urine in the collecting duck. And this basically is done without using too much energy. The only place we actually use energy is in the thick ascending loop of Henley. So within the thick ascending loop of Henley, we establish an electrochemical gradient by using ATP. And then in the descending loop of Henley, we utilize that electrochemical gradient to passively move water out of our tubial.