Why do some people need to use a dialysis machine? Explain the principal involved

Explanation

Dialysis machine is used to filter the blood of a person when two kidneys are damaged. The process is called 'haemodialysis'.
Principles involved in the process :

1) In this process blood is taken out from the main artery, mixed with an anticoagulant such as heparin and then pumped into the apparatus called dialyzer.
2) In this apparatus blood flows through channels or tubes. These tubes are embedded in the dialyzing fluid.
3) The membrane separates the blood flowing inside the tube and dialyzing fluid, which has the same composition as that of plasma, except the nitrogenous wastes.
4) The patients blood is passed through the tubes, during this passage the waste products from the blood pass into dialysing fluid by diffusion.
5) This process is called dialysis.
6) The purified blood is pumped back into the patient through a vein. This is similar to the function of kidney but it is different since there is no reabsoprtion involved.
7) Each dialysis session lasts for 3 to 6 hours. This method has been using for thousands of uremic/kidney failure patients all over the world.
Principle : Dialysis machine works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semipermeable membrane.