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.
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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