Bio 3 - Transportation of Substances around the body - Dialysis

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Dialysis

Your kidneys can be damaged or destroyed by infections. Some people may have a genetic problem meaning their kidneys fail, and sometimes kidneys could be damaged in an accident

Whatever the cause, untreated failure of Both Kidneys can lead to death. Toxins such as Urea build up in the body, and the salt and water balance of your body is lost

For centuries kidney failure meant certain death, but now we have two effective methods of treating it. One is Dialysis and the other is having a Kidney Transplant

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The machine that carries out the functions of the kidney is known as a Dialysis Machine. It relies on the process of dialysis to clean the blood. In a dialysis machine a persons blood leaves their body and flows between partially permeable membranes. 

On the other side of these membranes is the dialysis fluid. The concentration of the solutes in the dialysis fluid makes sure the unwanted substances pass out of the blood by diffusion. These include Urea and excess mineral ions. However, glucose and other useful substances stay in the blood.

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Without functioning kidneys, the concentration of Urea and mineral ions builds up in the blood. Treatment by dialysis restores the concentrations of these dissolved substances to normal levels. Then, as the patient carries on with normal life, Urea and other substances build up again. This means the dialysis has to be repeated at regular intervals

It takes around 8 hours for dialysis to be complete. So people with kidney failure have to remain attached to a dialysis machine for hours several times a week. They have to manage their diets carefully. This helps keep their blood chemistry as stable as possible

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During dialysis, it is vital that patients lose the excess Urea and mineral ions which have built up in their systems, and it is equally important that they do not lose substances such as glucose and useful mineral ions in their blood

The loss of these substances is prevented by the careful control of the dialysis fluid. It contains the same concentration of glucose and mineral ions as blood plasma so there is no net movement of glucose and useful mineral ions out of the blood. It also contains normal plasma levels of mineral ions so excess ions are lost from the blood along a concentration gradient, but no more.

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In contrast, dialysis fluid contains no urea, so there is a strong concentration gradient from the blood to the fluid for this substance, and all the urea leaves the blood.

The whole process of dialysis depends on diffusion along concentration gradients which have to be maintained by the flow of the fluid. There is no Active Transport.

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Many people go to hospital to receive dialysis, but in 1964 home dialysis machines were made available for the first time.

This meant that at least some people with Kidney Failure could set up their dialysis in their own home.

Even with all our modern technology, dialysis machines are still quite large, certainly much bigger than the kidneys they replace!

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Dialysis, however, has some disadvantages:

- You have to follow a very carefully controlled diet

- There are very long, regular sessions connected to a dialysis machine

- Over many years the balance of substances can become more difficult to control however careful the dialysis

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