Kidney Failure, Dialysis and Transplants

1. 1 State [1 mark]

   State what is meant by kidney failure.

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   Model answer

   The kidneys no longer filter the blood properly.

   Mark scheme

   • Kidneys do not filter the blood — 1 mark
2. 2 Name [2 marks]

   Name two substances that build up in the blood when the kidneys fail.

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   Model answer

   Urea and excess ions.

   Mark scheme

   • Urea — 1 mark
   • Excess ions, or excess water — 1 mark
3. 3 Describe [3 marks]

   Describe how a dialysis machine removes urea from the blood of a patient.

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   Model answer

   The blood flows along tubes with partially permeable walls, which are surrounded by dialysis fluid. The dialysis fluid has no urea, so the urea diffuses from the blood, through the membrane, into the fluid. The cleaned blood returns to the patient.

   Mark scheme

   • Blood flows next to a partially permeable membrane — 1 mark
   • Urea diffuses into the dialysis fluid — 1 mark
   • Cleaned blood returns to the patient — 1 mark
4. 4 Explain [3 marks]

   Explain why the dialysis fluid is changed during a treatment.

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   Model answer

   Urea diffuses from the blood into the dialysis fluid, and the concentration of urea in the fluid rises. If the fluid was not changed, the concentration gradient would fall, and the urea would stop moving. New fluid keeps the gradient steep.

   Mark scheme

   • Urea builds up in the fluid — 1 mark
   • Gradient falls without new fluid — 1 mark
   • New fluid keeps the gradient steep — 1 mark
5. 5 Explain [3 marks]

   Explain why a patient who has had a kidney transplant has to take drugs for the rest of their life.

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   Model answer

   The immune system of the patient recognises the antigens on the donor kidney as foreign, and attacks it, which is rejection. The drugs suppress the immune system, so the new kidney is not rejected.

   Mark scheme

   • Antigens on the donor kidney are foreign — 1 mark
   • Immune system attacks, which is rejection — 1 mark
   • Drugs suppress the immune system — 1 mark
6. 6 Evaluate [6 marks]

   A patient with kidney failure is offered either regular dialysis or a kidney transplant. Evaluate the two treatments.

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   Model answer

   Dialysis can be started at once, and it does not need a donor, so it keeps the patient alive while waiting for a kidney. But it takes three to four hours, about three times a week, it restricts the diet, and it is very expensive over many years, and it does not cure the problem. A transplant gives the patient a working kidney, so the patient is free of the machine, can have a more normal diet and life, and it is cheaper in the long run. However, there are too few donors, so the patient may wait a long time. There is a risk of rejection, so the patient has to take immunosuppressant drugs for life, which increases the risk of infection, and the operation is major. A transplant is generally better if a match can be found, but dialysis is needed while waiting.

   Mark scheme

   • Dialysis available at once — 1 mark
   • Dialysis disadvantages: time, diet, expense — 1 mark
   • Transplant gives a normal life — 1 mark
   • Transplant cheaper in the long run — 1 mark
   • Shortage of donors and rejection — 1 mark
   • Balanced conclusion — 1 mark

Quick check

1. 1

   What builds up in the blood in kidney failure?

   1. AOxygen
   2. BUrea and excess ions
   3. CGlucose
   4. DAntibodies
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   B: Urea and excess ions

   Urea and excess ions.

2. 2

   What does dialysis fluid contain?

   1. AUrea
   2. BOnly water
   3. CGlucose and ions at healthy concentrations, but no urea
   4. DBlood cells
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   C: Glucose and ions at healthy concentrations, but no urea

   Glucose and ions at healthy concentrations, but no urea.

3. 3

   How does urea leave the blood in dialysis?

   1. ABy diffusion through a partially permeable membrane
   2. BBy active transport
   3. CBy osmosis of blood
   4. DBy digestion
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   A: By diffusion through a partially permeable membrane

   By diffusion through a partially permeable membrane.

4. 4

   Why does the dialysis fluid contain glucose?

   1. ATo feed the machine
   2. BTo remove urea
   3. CTo dilute the blood
   4. DSo that glucose does not diffuse out of the blood
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   D: So that glucose does not diffuse out of the blood

   So that glucose does not diffuse out of the blood.

5. 5

   What is rejection?

   1. AThe kidney stops making urine
   2. BThe immune system attacks the donor organ
   3. CThe donor changes their mind
   4. DThe patient refuses surgery
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   B: The immune system attacks the donor organ

   The immune system attacks the donor organ.

6. 6

   Why do transplant patients take immunosuppressant drugs?

   1. ATo make urine
   2. BTo clean the blood
   3. CTo stop rejection of the new kidney
   4. DTo prevent diabetes
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   C: To stop rejection of the new kidney

   To stop rejection of the new kidney.

7. 7

   How often is dialysis usually needed?

   1. AAbout three times a week
   2. BOnce a year
   3. COnce a month
   4. DEvery minute
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   A: About three times a week

   About three times a week.

8. 8

   Which is an advantage of a transplant over dialysis?

   1. AIt is always available at once
   2. BNo drugs are needed
   3. CNo surgery is needed
   4. DThe patient can have a more normal life
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   D: The patient can have a more normal life

   The patient can have a more normal life.

9. 9

   Which is a disadvantage of kidney transplants?

   1. AThey need a machine
   2. BThere are too few donors
   3. CThey cost more than dialysis in the long run
   4. DThey are painful all the time
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   B: There are too few donors

   There are too few donors.