If one of your organs can’t do its job properly, you and the adults who look after you will go to hospital for the doctors to find out if you need to have an organ transplant.

You will probably stay in the hospital for a few days, so that you can have some tests to check that everything else inside your body is working fine. The doctors will test your urine, your blood and your poo, and you will also have X-rays and ultrasound. They might also give you an ECG and an EEG.

Sometimes, the doctors might take a biopsy of your damaged organ, so that they can see exactly how badly affected it is.

This is a list that has the names of all the kids who need an organ transplant. You go onto the transplant waiting list while doctors try to find an organ that is a good match for you. When an organ comes along from a donor who is the right match for you, the doctor phones you and your family so that you can come to hospital right away for your transplant.

Although organs from different people work in the same way, there are some differences between them. These differences are too small to see – they are differences in the antigens on the outside of cells. So, if the antigens on a new organ from a donor are completely different from those on your own organ, then your immune system might mistake your new organ for an invader and attack it! Don't worry though - your doctor will look for an organ from a donor whose antigens match your antigens.

The size and age of the donor is also important in matching. For example, a big heart wouldn’t fit into a small body, and a small heart wouldn’t pump enough blood for a big body!

Once an organ has been removed from a donor, is has to be transplanted quickly so that it will still work. If the donor isn’t in the same hospital as you, it will be sped to you by motorbike, car, helicopter or even aeroplane!

During this time, you’ll have some tests to make sure you’re ready for surgery – things like blood tests, chest X-rays and an ECG.

If everything is OK you’ll be taken to a room called an operating theatre where the transplant will take place. You be given a general anaesthetic to send you into a deep sleep during the operation. Then the surgeon will go inside and disconnect all the plumbing and blood vessels from your old organ.

The new organ will be inserted once the old organ has been removed, and all the pipes and blood vessels will be reconnected. When everything’s finished, the surgeon sews up the cut they made to get inside you, and you’ll wake up later not remembering a thing!

An organ transplant is a big operation, and you’ll have to stay in hospital for some time afterwards so the doctors can check to make sure everything went OK.

Unless the donor is your twin, finding an exact match is very unlikely. This means that your new organ will still have some foreign antigens, so your immune system might still attack it. This is called transplant rejection. To stop this from happening, your doctor will give you medicines called immunosuppressant. If the Immunosuppressant can’t stop the transplant rejection, you may need to have a bone marrow transplant.

If you have any other questions, you can ask your doctor, or chat to other people who are having an organ transplant in the Medikidz forums and virtual world, Mediland.