Dialysis: Artificial Removal of Waste

Excretion is a metabolic process that involves the removal of excess waste from our body. In vertebrates, lungs, kidneys, and skin perform the function of excretion. It is an essential part of human physiology.

Kidneys are a paired structure found in the human body that removes excess waste, such as water, solutes and toxins. However, in some cases, kidneys fail to do so, and then the person has to undergo dialysis meaning artificial removal of waste from the body. Dialysis is an artificial procedure for the removal of waste from the body. It is a temporary solution for people who are awaiting kidney transplantation. But in some cases, it is a permanent solution too.

Principle of Dialysis

Dialysis works on the principle of diffusion and ultrafiltration. Diffusion is a process where a substance moves from its higher concentration to a lower concentration via a semipermeable membrane. A semipermeable membrane is a thin layer with various holes of different sizes. In dialysis, blood flows on one side of the semipermeable membrane and a special dialysate moves in the flows on the opposite side.

The membrane allows smaller molecules and water to pass through it but retains larger molecules such as red blood cells and proteins. This way, the ultrafiltration process of the kidney is replicated through the process of dialysis.

Types of Dialysis

There are five types of dialysis, three of which are primary and two are secondary. Let us look at them in detail.


It is a primary type of dialysis. In haemodialysis, blood is exposed to a partially permeable membrane in a dialyzer. The dialyzer is made up of small synthetic hollow fibres that act as the semipermeable membrane. The blood flows through the fibres, and dialysate flows around the fibres. The solutes, waste and water move between the two solutions.

Ultrafiltration of the blood is carried out by increasing the negative hydrostatic pressure across the membrane. This pressure allows waste and toxic materials from the blood to flow in the direction of dialysate. The filtered blood is transferred back to the body.

Peritoneal dialysis

In this type, the dialysate is a sterile solution containing glucose that is passed through a tube into the peritoneal cavity, the abdominal cavity around the intestine. The peritoneal membrane acts as the semipermeable membrane through which the solutes and water molecules pass through. This process is less efficient than haemodialysis.


It is a process that is similar to haemodialysis, but it does not use any dialysate. In this procedure, the blood is pumped through a hemofilter, and a pressure gradient is applied. This gradient moves water and solutes across the membrane rapidly along with larger molecules that are usually not carried in haemodialysis.


It is a secondary process of dialysis that is a combination of hemodialysis and hemofiltration.

Intestinal dialysis

In intestinal dialysis, the patient’s diet is supplemented with lots of fibres, such as acacia fibres, that are digested by bacteria in the colon. This leads to an increase in the amount of nitrogen in the faecal waste produced.

Respiration and Renal Failure

Kidney failure or renal failure is a condition where the kidneys cannot filter the waste products from the blood effectively and function at less than 15% of normal levels. Renal failure also affects the respiratory system. Functioning of the kidney and lungs are intimately related. Diseases that affect both the lungs and kidneys include glomerulonephritis and alveolar haemorrhage. Renal failure is often accompanied by respiratory complications, such as pulmonary edema, pulmonary calcification and often sleep apnea.

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