Urea can be removed by the process called hemodialysis in patients suffering from uremia. Blood drained from a convenient artery is pumped into a dialysing unit after adding an anti coagulant like heparin. The unit contains a coiled cellophane tube surrounded by a fluid having the same composition as that of plasma except the nitrogenous waste.
The porous ceilophare membrane of the tube allows the passage of molecules based on concentration gradient. As nitrogenous wastes are absent in the dialysing fluid, these substances freely move out, thereby clearing the blood. The cleared blood is pumped back to the body through a vein after adding anti heparin to it.