Haemodialysis is the artificial process by which urea is removed from the body of the patient.

i. Blood drained from an artery is
pumped into a dialysing unit after the addition of anticoagulant like heparin.

ii. The unit contains a coiled cellophane tube surrounded by a dialysing fluid having the same composition as that of plasma except the nitrogenous wastes. 

iii. The porous cellophane membrance 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.

iv. The cleared blood is pumped back to the body through a vein after adding anti-heparin to
it. This method is a boon for thousands of uremic patients all over the world.