Triple Science Only - Kidney Transplants And Kidney Dialysis
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of the kidney.
What toxic waste product do the kidneys remove from the blood?
Urea
What happens if the kidneys stop working properly?
Urea builds up in the blood, which can be fatal.
What are the two main treatments for kidney failure?
Kidney dialysis and kidney transplant.
Topic Explainer Video
Check out this @lauradoesbiology video that explains kidney dialysis, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Kidney Dialysis & Transplants
Why Kidney Failure Is Dangerous
- If both kidneys fail, toxic waste (like urea) builds up in the blood.
- This can lead to death unless treated by:
-
Dialysis
-
Kidney transplant
-
Kidney Dialysis – How It Works
A mechanical method of filtering the blood in place of the kidneys.
Key Features:
- Patient’s blood is passed through a dialysis machine.
- Blood flows through tubes with partially permeable membranes, which mimics a real kidney.
- Outside of the tubes is dialysis fluid which contains:
- No urea.
- Correct levels of glucose, water and mineral ions.
What happens:
- Urea and excess ions / water diffuse out of the blood, through the partially permeable membranes, and into the dialysis fluid. They are small enough to pass through the membrane and move down their concentration gradient.
- Glucose and other useful substances remain in the blood.
- Glucose will remain in the blood as the dialysis fluid contains the same concentration of glucose as the blood, this means there is no concentration gradient.
- Proteins and blood cells will remain in the blood because they are too large to pass through the partially permeable membrane.
This maintains normal blood composition and removes waste, including all urea.
Things to consider
Dialysis is used when a patient with kidney failure is waiting for a suitable donor for a kidney transplant. It removes toxic urea from the patient’s blood to keep them alive. However, It has many disadvantages.
- Dialysis must be done 3 times per week, for 3–5 hours each session, usually in a hospital. This can affect a patients quality of life as it puts restrictions on activities such as travelling, going on holiday or attending work.
- If patients don’t live near to a hospital it can also add additional travel time and transport to hospital may be expensive.
- Between dialysis sessions, levels of urea will build up in the patients blood which can make them feel unwell.
- Patients need to carefully monitor their diet and restrict the amount of protein eaten to make sure levels or urea do not increase too much. (Remember, urea is made from excess amino acids!)
- During dialysis, a needle is put into the patients arm to draw out their blood- this carries a risk of infection.
- Patients need to take anti- clotting medication to reduce their risks of developing a blood clot during dialysis treatment.
Kidney Transplants – The Biological Option
Replacing a failed kidney with a working donor kidney. This is a permanent solution.
Advantages:
- No regular dialysis needed, so far fewer hospital visits.
- Allows a more normal lifestyle with no restrictions on diet and day to day activities.
- Cheaper in the long term for the NHS / hospitals.
- The new kidney will maintain low levels of urea in the blood.
Disadvantages:
- Risk of rejection – the immune system may attack the new kidney.
- Patient must take immunosuppressant drugs for life which weakens their immune system, this puts them at risk of other infections.
- Limited supply of suitable donors and a long waiting list.
- Surgery risks (infection, anaesthetic and damage to the new organ).
- Recovery from surgery may take a long time.
Key Terms & Definitions
|
Key Term |
Definition |
|---|---|
|
Urea |
A toxic waste product made in the liver from excess amino acids. |
|
Dialysis |
A process that filters waste products from the blood, such as urea, using a machine. |
|
Partially permeable membrane |
A barrier that allows small molecules (like urea) to pass through but not others (like proteins). |
|
Kidney transplant |
A surgical procedure to replace a failed kidney with a healthy donor kidney. |
|
Immunosuppressant drugs |
Medicines that reduce the immune response to prevent organ rejection. |
No answer provided.
Exam Tips
When asked to evaluate dialysis vs transplant, include:
- Both advantages and disadvantages- look at the number of marks to guide you as to how many you should write.
- If provided with some information in the exam question itself you can use this in your answer but you must add value to it. This means further explanation of each advantage or disadvantage. Don’t just copy exactly what the examiner has already given you!
No answer provided.
Practice Questions
Doctors sometimes give patients dialysis treatment, rather than a kidney transplant.
Suggest four reasons for this. (4 marks)
Model Answer:
any four from:
• no need for taking immunosuppressants
• no rejection chance
• no / less risk during surgery / no risk of anaesthetic
• operation may be unsuitable / risky for older age patients
• less risk of infection
• suitable for short term
• no suitable kidneys may be available for transplant / there is a long waiting list for a donor kidney
• less painful than major surgery
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!