The Kidneys

Your kidneys form part of your urinary system -
making urine from the waste products and excess water found in your blood.
They are dark red, roughly fist-sized and sit below the ribcage towards the back of your body.

Kidney transplant facts

You can live healthily with one functioning kidney
When a kidney is removed, the remaining normal kidney will increase in size to compensate for the loss of the donated kidney.

Common reasons for transplantation

Kidney transplants are needed as a result of end-stage kidney disease. There are several possible treatments for kidney failure including dialysis. The most common causes of chronic kidney failure are:

  • Primary kidney disease
  • Diabetes mellitus
  • Infection
  • High blood pressure

How they work

Your kidneys play a vital role in regulating your blood composition. Inside your body, the water, acid levels (pH) and salt levels need to be kept constant and your kidneys play a part in this by filtering huge volumes of blood as it passes round the body.

Blood is carried into the kidneys by the renal artery. You will have around one to one and a half gallons of blood circulating through your body and your kidneys filter that blood as many as 400 times a day. The blood enters your kidney and is distributed to tiny filtration units known as nephrons. These nephrons filter substances like water, salts, acids and alkalis out of your blood and then reabsorb some of them. It is this secretion or reabsorbtion that keeps your blood composition constant.

Excess water and waste products are then secreted as urine. Urine passes from the kidney, though a tube called the ureter, to the bladder. The amount of urine is constantly managed by your kidneys to maintain your blood composition. If you don't have enough fluid in your body, the brain communicates with the kidneys by sending out a hormone that tells the kidneys to hold on to some fluids. When you drink more, this hormone level goes down, and the kidneys will release more.



When kidneys go wrong

People can live healthily with one functioning kidney. However, when about 90% of kidney function has been lost, a person can only survive by having dialysis. Dialysis works by using a machine that replicates the blood-cleaning function of healthy kidneys. In the most extreme cases of kidney failure, survival depends on the person receiving a donor organ.

Diabetes mellitus, a condition causing high blood sugar levels, is the most common cause of kidney transplantation. Other causes include high blood pressure and some infections.



Your kidney's other functions

In addition to balancing the volume of fluids and minerals in the body (a principle called homeostasis), your kidneys have other functions. They constantly react to hormones that the brain and other organs sends them. For example, when your kidneys detect that your blood pressure is dropping, they secrete an enzyme called renin. This enzyme triggers a chain of events that makes your kidneys reabsorb more salt and water, leading to an increase in blood pressure.

Your kidneys even make some of their own hormones. For example, the kidneys produce a hormone that tells the body to make red blood cells.

Kidney transplants

A kidney transplant involves the transfer of a healthy kidney into the body of a person who has little or no kidney function.



History and progress of kidney transplantation

Early transplantation research involving the kidneys of animals was taking place in Europe and North America at the turn of the twentieth century. Arguably the first 'successful' human kidney transplantation was performed on June 17, 1950, in the United States. The operation involved the transplantation of one kidney from a non-living (deceased) donor, and although the donated kidney was rejected ten months later, the transplant was deemed successful because the intervening time gave the remaining kidney time to recover. The patient went on to live for more than four years after the operation, resumed an active lifestyle, and died of a heart attack - unrelated to the transplant.



Living Donors

Most transplants are from a donor who is dead, but in some cases a living person may donate. Kidneys from these donors must be compatible in size with the recipient and have a matching blood group. A live organ can come from a family member, a friend or even from a stranger. Thanks to improved medications, a very close genetic similarity between the donor and recipient is no longer required to ensure a successful transplant.

However, kidney donors must have a blood type that is compatible with the recipient. In living donation, the following blood types are compatible:

Donors Recipients
blood type A blood types A and AB
blood type B blood types B and AB
blood type AB blood type AB Only
blood type O blood types A, B, AB and O
(O is the universal donor: donors with O blood are compatible with any other blood type)
Recipients Donors
blood type O blood type O only
blood type A blood types A and O
blood type B blood type B and O
blood type AB blood types A, B, AB and O
(AB is the universal recipient: recipients with AB blood are compatible with any other blood type)


Any person who wishes to donate a living kidney must undergo careful and thorough evaluation and the donation must be completely voluntary.

When a living donor wishes to donate, but is incompatible with the recipient, it is possible to join a paired exchange.



Paired kidney donation

Sometimes a loved one may want to donate a kidney but their blood type is incompatible. In this case it may be possible to pair up with another incompatible donor and recipient and arrange a 'swap'. If the recipient from one pair is compatible with the donor from the other pair, and vice versa - two simultaneous transplants can take place.



A donor chain

Donor chains can involve many more donors and recipients. It starts with one kind donor who volunteers a kidney - this kidney is then transplanted to a recipient who had a willing donor but was not a match. The second willing donor then donates to a compatible patient they do not know - and the chain can continue.

For more information about becoming a living donor for kidney transplantation or for our FAQs about living kidney donation, please see the links below:


Becoming A Living Donor >
FAQs >

Mini Glossary

  • Dialysis:
    A method of cleaning the blood generally using a machine.
  • Homeostasis:
    The controlling and stabilising of the body's condition in reaction to external changes.
  • Nephrons:
    Tiny filters inside the kidney that remove waste.
  • Renal:
    Of or relating to the kidneys.
  • Ureters:
    Tubes that carry the urine from each kidney to the bladder.
  • Urethra:
    A tube that carries the urine from the bladder out of the body.

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