12.5 Kidney Transplants

A free GCSE Biology lesson for AQA (8461) from OBA School: how transplants treat kidney failure, preventing rejection, and comparing transplants with dialysis. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe how a kidney transplant treats kidney failure
• Explain why a donor kidney may be rejected and how rejection is prevented
• Compare dialysis and transplants using data, including costs
• Evaluate the advantages and disadvantages of kidney transplants

Key words

• Transplant: Replacing a failed organ with a healthy one from another person (the donor).
• Donor: The person who gives the organ. Kidney donors can be living or can have died.
• Antigens: Proteins on the surface of cells. The immune system recognises antigens it does not know as foreign.
• Rejection: When the recipient’s immune system attacks the transplanted organ.
• Tissue matching: Choosing a donor whose antigens are as similar as possible to the recipient’s.
• Immuno- suppressant: A drug that weakens the immune system so it is less likely to attack the new organ.

What a kidney transplant involves

A healthy kidney from a donor is placed in the lower abdomen and joined to the patient’s blood vessels and bladder. The failed kidneys are usually left in place. One working kidney is enough to keep a person healthy.

• Living donors are often close relatives. A healthy person can live normally with one kidney.
• Deceased donors have died, often in hospital, and agreed (or did not opt out) to donate their organs. England, Wales and Scotland now use an opt-out system.

Key fact: A transplant can restore normal kidney function, so no dialysis is needed. It usually works for many years (often 10–25), but may eventually need replacing.

Rejection and how to prevent it

The cells of the donor kidney carry antigens that differ from the patient’s own. The patient’s immune system may treat the kidney as foreign and attack it. This is rejection.

Worked example: explain a choice of donor

Why is a brother or sister often a good kidney donor?
Siblings inherit genes from the same parents, so their tissue type (antigens) is more likely to be similar.
This reduces the risk of rejection, so a lower dose of immunosuppressant drugs may be needed.

Answer: a closer tissue match means less risk of rejection

Measuring kidney function

Doctors estimate the glomerular filtration rate (GFR) – roughly how many cm³ of blood the kidneys filter each minute – from a blood test. It is used to decide when dialysis or a transplant is needed. (Background only: you do not need to learn these values for AQA.)

• 90 or more; Kidney function Normal
• 60–89; Kidney function Mildly reduced
• 30–59; Kidney function Moderately reduced
• 15–29; Kidney function Severely reduced
• below 15; Kidney function Kidney failure – dialysis or a transplant is needed

Worked example: rate of decline

A patient’s GFR fell from 52 to 16 over 4 years. Calculate the mean fall per year.
(52 − 16) ÷ 4 = 36 ÷ 4 = 9 per year.
If it keeps falling at this rate, it drops below 15 within the next year.

Answer: 9 cm³ per minute each year

Transplant or dialysis?

Worked example: using Figure 2

Cost over 10 years: dialysis = 10 × £30 000 = £300 000. Transplant = £20 000 + 10 × £6000 = £80 000.
Saving = £300 000 − £80 000 = £220 000.
The lines cross when 30 000t = 20 000 + 6000t, so t = 20 000 ÷ 24 000 ≈ 0.83 years (about 10 months).

Answer: £220 000 saved per patient over 10 years

• Daily life; Transplant Near-normal life, diet and travel; Dialysis About 12 hours a week on a machine; strict diet
• Long-term cost; Transplant Lower after the first year; Dialysis High every year
• Availability; Transplant Not enough donors; can wait years; Dialysis Available as soon as needed
• Risks; Transplant Surgery, rejection, infections from immunosuppressants; Dialysis Infections, blood clots; urea and ion levels swing

Common mistakes

• Saying a kidney is rejected because it is the "wrong size". It is caused by different antigens.
• Forgetting that immunosuppressants are needed for life and make infections more likely.
• Saying a transplant is always better, ignoring donor shortages, surgery and rejection.

Revision questions

Try these, then check your answers below each one.

Question 1. Why might a patient’s body reject a donor kidney? (Choose from: Its cells have different antigens, so the immune system attacks it, It is the wrong size for the body, The donor had a different blood glucose level, It contains no nephrons.)

Answer: Its cells have different antigens, so the immune system attacks it

Working: The donor cells carry antigens the patient’s immune system recognises as foreign, so white blood cells attack the kidney.

Question 2. Name the type of drug a transplant patient takes to reduce the risk of rejection.

Answer: immunosuppressant

Working: Immunosuppressant drugs weaken the immune system so it is less likely to attack the new kidney.

Question 3. True or false? Immunosuppressant drugs make a transplant patient less likely to catch infections.

Answer: False

Working: False. They weaken the immune system, so the patient is MORE likely to catch infections.

Related lessons

• Previous lesson: 12.4 Dialysis – an Artificial Kidney
• Next lesson: 13.1 Types of Reproduction
• In this chapter: 12.1 Controlling Body Temperature
• In this chapter: 12.2 Removing Waste Products
• In this chapter: 12.3 The Human Kidney

Continue in the full course

This lesson is section 12.5 (AGCBH1205) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.