Unit 3 - Dialysis
A major problem with kidney transplants is tissue rejection.

Unit 3 - Dialysis

Patients suffering from kidney failure may have to undergo the process of dialysis. Understanding how dialysis works will also give GCSE Biology students an understanding of how the kidneys function in healthy people.

The kidney controls and regulates the level of water and the balance of ions in the blood. If a person suffers from kidney failure, their means of blood regulation is lost and the level of the toxic chemical urea builds up in their blood. Urea is normally eliminated from the body in the urine. High levels of urea can be fatal and there are two choices for patients - a kidney transplant or dialysis. There are many reasons why kidney failure occurs, such as high blood pressure, infection, diabetes and inherited conditions.

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The process of dialysis involves the patient being connected to a dialysis machine several times a week to restore the balance of the blood and to remove the deadly urea. During dialysis, blood is removed from the patient via a tube, mixed with blood thinners to prevent clots forming and pumped into the dialysis machine. Here, the blood passes a partially permeable dialysis membrane. On the opposite side of the membrane, dialysis fluid is pumped past, which sets up a concentration gradient across the membrane in the machine. The concentration gradient causes diffusion of the various ions in the blood, including urea. The dialysis fluid must therefore contain concentrations of ions and glucose similar to that in normal blood and no urea. Movement of the glucose and ions therefore only occurs if there is an imbalance.

As the ions and water diffuse through the membrane into the dialysis fluid, the concentration gradients of the different ions and water across the dialysis membrane reduces. It takes several hours for the gradients to reduce to zero, at which time, the blood has been cleaned. The patient can then live an almost normal life for a few days before the next dialysis is required.

Dialysis is a very time consuming process and is used when patients have kidney failure. Usually, the only chance for a normal healthy life is a kidney transplant. There are several advantages and disadvantages to dialysis such as an increased risk of infection and the need for a special diet between dialysis procedures, but dialysis machines can be installed at the patient's home and can keep them alive until a kidney transplant is available.

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  1. Dialysis is needed when which organ(s) fails?
    Dialysis is specific to the kidneys
  2. Dialysis removes this waste material from the blood.
    It also restores the balance of ions and water in the blood, but the removal of urea is extremely important as it is toxic
  3. The dialysis membrane is...
    Only small molecules, such as urea and certain ions, can pass out of the blood. Essential, large molecules like proteins must remain in the blood and are too big to pass through
  4. Dialysis relies on movement of molecules and ions by the process of...
    Urea will cross the dialysis membrane by diffusion because the dialysis fluid is carefully designed to create the correct concentration gradient across the membrane
  5. Urea travels from...
    This is done by making sure that the concentration of urea in the dialysis fluid is lower than in the blood of the patient
  6. To retain glucose and ions in the blood, their concentration in dialysis fluid will be...
    Blood glucose concentration must be the same is in the dialysis fluid, otherwise glucose would be lost or gained from the patient
  7. One major problem with dialysis is...
    The patient must remain connected to the machine for many (usually for about 4 - 6) hours and it needs to be carried out regularly, every few days
  8. Apart from dialysis, another treatment for kidney failure is a...
    Finding a suitable donor can be time consuming
  9. A major problem with kidney transplants is...
    The kidney to be transplanted must have similar antigens to the patient. The process of finding a suitable organ for any transplant, including a kidney transplant, is called tissue typing
  10. To avoid tissue rejection, the kidney transplant patient has to take drugs which suppress which system of the body?
    After a transplant, the patient will need to take drugs that suppress the immune system to reduce the chances of it attacking the new kidney and damaging or destroying it. This leaves transplant patients more vulnerable to any infection

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