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Topic last updated: 30 Sep 2021
    • Biologybiology Biology
    • Ico Human Biology Human biology
    • Ico Physical Education Physical education
    • 14-16
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    • 55

Homeostasis - kidneys and water balance

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Kidney transplants


If the kidneys fail completely they may be replaced by a kidney transplant. In a transplant the functions of the failing kidneys are taken over by a single healthy kidney from a donor. The donor kidney is joined to the blood vessels and the bladder in the groin of the patient (the recipient) and shortly after a successful transplant urine begins to flow from the new kidney. If all goes well the transplanted kidney will function normally in its new body, cleaning and balancing the blood.

One kidney is enough to remove the waste urea and balance the blood of an individual for the rest of their lives. However, most transplanted kidneys only last about 9 years. Once they begin to fail again the patient will have to return to dialysis or have another transplant if a donor becomes available.



One big problem is rejection. The protein markers (antigens) on a kidney are usually different from a patient's protein markers. The patient's immune system detects this difference and may reject the new kidneyImmunosuppressant medicines are used to suppress the immune system to prevent rejection.


In a transplant operation the new kidney is attached to the blood vessels and bladder but the old kidneys are often left in place as well, in case they recover some of their function.

Human organs are filled with cold fluids and transported in chilled containers to keep them healthy so they will work again once they have been transplanted.


Finding donors

The other big problem with kidney transplants is that there are not enough donors to go around. In the UK alone about 2500 transplants are carried out each year but there are still around 7000 people on dialysis waiting for a transplant. Most kidneys come from people who have died in an accident or have died suddenly from a stroke or similar event. Better car safety and better medicine mean fewer people are dying - good news but giving fewer donors. More healthy people are choosing to donate one of their kidneys to someone with kidney failure. They are known as living donors. In future stem cell technology may allow us to grow new kidneys for anyone who needs them.