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This lesson covers what happens when the kidneys fail and the treatments available — dialysis and kidney transplants. You need to understand how each treatment works, their advantages and disadvantages, and be able to evaluate them for Edexcel GCSE Biology (1BI0) Topic 7.
Kidney failure (also called renal failure) is when the kidneys can no longer adequately filter the blood. This means:
| Cause | Detail |
|---|---|
| Diabetes | Prolonged high blood glucose damages the tiny blood vessels in the kidneys |
| High blood pressure | Damages the delicate filtering structures (glomeruli) |
| Infections | Severe or repeated kidney infections can cause permanent damage |
| Genetic conditions | Some inherited conditions (e.g. polycystic kidney disease) cause kidney failure |
| Physical injury | Trauma or reduced blood supply to the kidneys |
When kidneys fail, an artificial method of filtering the blood is needed. This is called dialysis. There are two main types.
Haemodialysis is the most common form of dialysis. Blood is taken from the patient's body, passed through a machine that filters it, and then returned to the body.
| Substance | What Happens | Why |
|---|---|---|
| Urea | Diffuses out of the blood into the dialysis fluid | Urea concentration is high in blood and zero in fresh dialysis fluid → moves down its concentration gradient |
| Excess ions | Diffuse out of the blood into the dialysis fluid | Concentration gradient from blood to fluid |
| Glucose | Stays in the blood | Dialysis fluid contains the same concentration of glucose as normal blood → no net movement |
| Useful ions | Remain at normal levels | Dialysis fluid is carefully formulated to contain normal concentrations of essential ions, so there is no net loss |
| Blood cells and proteins | Stay in the blood | Too large to pass through the partially permeable membrane |
Exam Tip: The key principle is diffusion down a concentration gradient. Waste products move from the blood (high concentration) into the dialysis fluid (low concentration). Useful substances are maintained because the dialysis fluid is designed to match the normal blood concentration of these substances.
| Feature | Detail |
|---|---|
| Frequency | Usually 3 sessions per week |
| Duration | Each session lasts approximately 3–4 hours |
| Location | In a hospital dialysis unit or at home (with a home dialysis machine) |
| Access | A special connection (fistula) is created in the arm to allow easy connection to the machine |
Peritoneal dialysis is an alternative to haemodialysis. Instead of using an external machine, the patient's own peritoneum (the membrane lining the abdominal cavity) is used as the filter.
| Feature | Detail |
|---|---|
| Frequency | Fluid exchanges performed several times a day (or continuously overnight using a machine) |
| Location | Can be done at home or at work |
| Advantage over haemodialysis | Greater flexibility; does not require hospital visits |
| Disadvantage | Risk of infection at the catheter site; less efficient per session than haemodialysis |
Although dialysis keeps patients alive, it has significant limitations:
| Limitation | Detail |
|---|---|
| Time-consuming | Haemodialysis requires 3–4 hours, 3 times per week; this significantly impacts daily life |
| Dietary restrictions | Patients must carefully control their intake of salt, potassium, phosphorus, and fluids |
| Does not cure kidney failure | Dialysis replaces kidney function temporarily; it must be continued for life (unless a transplant is received) |
| Side effects | Fatigue, low blood pressure, muscle cramps, and itching are common |
| Risk of infection | Haemodialysis fistula sites and peritoneal catheters can become infected |
| Reduced quality of life | Many patients report that dialysis significantly limits their social life, work, and travel |
| Costly | Long-term dialysis is very expensive for healthcare systems |
A kidney transplant involves surgically replacing a failed kidney with a healthy kidney from a donor. This is generally considered the best long-term treatment for kidney failure.
| Donor Type | Detail |
|---|---|
| Living donor | A healthy person (often a close relative) donates one of their two kidneys. Humans can live a normal life with one kidney |
| Deceased donor | A kidney is taken from a person who has recently died (and who consented to organ donation) |
The biggest challenge with transplants is the risk of rejection — where the patient's immune system recognises the new kidney as "foreign" and attacks it.
| Strategy | Detail |
|---|---|
| Tissue matching | The donor kidney must have antigens that closely match the patient's antigens. Close relatives (especially siblings) are more likely to be a good match |
| Blood type matching | The donor and recipient must have compatible blood types |
| Immunosuppressant drugs | The patient must take drugs that suppress the immune system for the rest of their life, reducing the chance of the immune system attacking the new kidney |
| Problem | Detail |
|---|---|
| Increased infection risk | A suppressed immune system is less able to fight off pathogens (bacteria, viruses) |
| Must be taken for life | Missing doses increases the risk of rejection |
| Side effects | Long-term use can cause high blood pressure, increased cancer risk, and other health issues |
| Increased vulnerability to illness | Patients must take extra care to avoid infections |
Exam Tip: When discussing kidney transplants, always mention tissue matching (antigens must be similar), immunosuppressants (must be taken for life), and the risk of rejection. These are the three key points examiners look for.
| Feature | Dialysis | Kidney Transplant |
|---|---|---|
| How it works | Artificially filters the blood using a machine or the peritoneum | Replaces the failed kidney with a healthy donor kidney |
| Effectiveness | Replaces some kidney function; not as efficient as a real kidney | A healthy transplanted kidney functions like a normal kidney |
| Duration of treatment | Ongoing; must continue for life (unless transplant received) | One-off surgery; the transplant can last 15–20+ years |
| Impact on daily life | Significant — regular sessions, dietary restrictions, fatigue | Much less — after recovery, patients can live relatively normally |
| Risks | Infection at access site, blood pressure problems, fatigue | Rejection, infection risk (immunosuppressants), surgical risks |
| Availability | Widely available; no waiting list | Limited by donor availability; long waiting lists |
| Medication | No immunosuppressants needed | Must take immunosuppressants for life |
| Cost | Expensive long-term (ongoing sessions) | Expensive initially (surgery) but cheaper long-term |
| Quality of life | Lower | Higher |
| Cures kidney failure? | No — manages it temporarily | Effectively yes (as long as the transplant functions) |
Exam Tip: If asked to evaluate dialysis versus transplant, give advantages and disadvantages of both. A common conclusion is that a transplant provides a better quality of life, but it depends on donor availability, tissue matching, and the patient's overall health.
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