The kidneys eliminate the body’s metabolic wastes. However, the kidneys may fail eventually due to some underlying illness or senility.  In these cases, dialysis means the difference between life and death. Here, let’s learn about the concept of dialysis with a well-labelled diagram.

Dialysis Meaning

“Dialysis is an artificial way to eliminate waste and excess fluid from the body.”

Dialysis is carried out when the kidney does not function normally. It is a process that eliminates wastes and excess fluid from the blood. If left untreated, waste products and fluids can get accumulated in the body at dangerous levels.

Table of Contents

What is Dialysis?

A kidney can filter 100-150 quarts of blood every day. If the kidneys are not functioning properly, waste starts accumulating in the blood. This results in coma and even death.

To cure this, the patient is subjected to dialysis. Dialysis maintains the body balance in the following ways:

  • It controls blood pressure.
  • It removes excess water and metabolic wastes from the body.
  • Prevents chemicals such as potassium, bicarbonate and sodium from reaching hazardous levels.

Dialysis is done when a person is suffering from a critical kidney disorder – grave kidney damage or previously severe renal failure. It is required when the kidney loses 90% of its efficiency and has a glomerular filtration rate of less than 15. This treatment may continue for months or years since most kidney failures are irreversible.

Also Read: Disorders of Excretory System

Principle of Dialysis

Dialysis involves the process of ultrafiltration of fluid through a semipermeable membrane and concept of the dissipation of solutes. Diffusion is a characteristic of materials in water that has the tendency to flow against a concentration gradient.

Blood runs on one flank of the semi-permeable film, and dialysate or distinct dialysis fluids flow on the opposite flank. A selectively permeable layer is a skinny membrane of material that comprises pores of different sizes or holes.

Minor solutes and fluids flow through the layer, but the membrane stops the path of bigger substances (for instance, large proteins, red blood cells). This imitates the filtering procedure that happens in the kidneys when the blood moves into the kidneys and the bigger substances are divided from the minor ones in the glomerulus.

However, dialysis is not a permanent solution, instead, it should be seen as a temporary alternative to substitute the kidney’s function until the kidney can repair itself. But chronic kidney damage will rarely heal itself, the only solution being a kidney transplant.  Typically, patients have a longer life expectancy if they opt for a kidney transplant than dialysis.

Dialysis – Diagram


Dialysis – Mechanism

  • The arterial blood is passed through the dialyser and then back to the body through the vein. Heparin is used as an anticoagulant while passing the blood through the machine.
  • Inside the dialyser, the blood moves through the hemofilter, which contains tiny channels that are interposed between two cellophane membranes. These are porous membranes
  • The outer surface of these membranes is bathed in the dialysing fluid called dialysate. The used dialysate is constantly replaced by fresh dialysate. 
  • Urea, phosphate, creatinine, and other unwanted substances from the blood pass into the dialysate by the concentration gradient. The essential substances required by the body diffuse from the dialysate into the blood. 
  • Except for plasma proteins, almost all substances are exchanged between the blood and dialysate through the cellophane membranes. 
  • The dialysis machine also has several blood pumps with pressure monitors that enable easy flow of blood from the patient to the machine and back to the patient. It also has pumps for the flow of fresh dialysate and for drainage of used dialysate. 

Types of Dialysis

There are two types of dialysis:


In this method, the patient’s blood is passed through the dialysis machine where it is purified and returned to the patient’s body.

Peritoneal dialysis

Peritoneal dialysis is done by surgically implanting a catheter in the stomach of the patient. A cleaning fluid (dialysate) is then circulated throughout the catheter that absorbs the waste materials from the blood vessels in the walls of the stomach. It is then drawn out and discarded. Peritoneal dialysis is considered to be more versatile and convenient than hemodialysis.

Also Read: Peritoneal Dialysis

Advantages of Dialysis

  • Dialysis can be carried out even at home.
  • Peritoneal dialysis is a comfortable method of dialysis that is easy to use.
  • The equipment used in peritoneal dialysis is less bulky and easy to carry along with the patient.
  • Unlike peritoneal dialysis, hemodialysis is not be carried out every day.

Also Read: Human Excretory System

To learn more about dialysis, its meaning, types and advantages or any other related topics, keep visiting BYJU’S website.

Frequently Asked Questions


What do you mean by dialysis?

Dialysis involves the process of removing wastes and excess fluid from the body.


When is dialysis required?

Dialysis is required when the kidney is unable to filter waste from the blood. This may be due to certain acute and chronic diseases, exposure to toxic pollutants, or certain medications.


Why dialysis is done?

Dialysis is done when a person is suffering from kidney failure. In such a scenario, kidneys don’t filter blood and as a result, toxins and wastes are built up in the bloodstream. Thus dialysis is done.


Is dialysis a temporary treatment for kidney diseases?

Dialysis serves as a temporary treatment until the kidneys repair themselves and start functioning properly. However, in chronic cases, the kidneys cannot repair themselves. In fact, the condition starts getting worse. In such a case, the patient needs dialysis regularly.


How are hemodialysis and peritoneal dialysis different from each other?

In hemodialysis, blood is pumped out of the body, filtered through a machine and returned to the body through the tubes that connect the patient to the machine. On the contrary, in peritoneal dialysis, a catheter is implanted in the patient’s stomach through which the dialysate is circulated. This dialysate absorbs all the waste from the body.

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  1. Educative

  2. Very Nice way to explain and it was really helpful to me

  3. Hi I am subhas