Hormones: Maintaining Blood Homeostasis (AQA GCSE Biology): Revision Notes
Kidney treatments
When someone has kidney failure, their kidneys can't philtre waste from their blood properly. There are two main ways doctors can treat this serious condition.
Kidney failure is a life-threatening condition that requires immediate medical treatment. Without intervention, waste products build up in the blood and can cause serious health complications.
Organ transplant
An organ transplant means putting a healthy kidney from a donor into a patient who needs it. This is done through surgery.
How transplants work
A healthy person can donate one of their kidneys because we can live normally with just one kidney. The donated kidney is surgically placed into the patient's body and connected to their blood supply.
The rejection problem
The biggest challenge with kidney transplants is that the body's immune system tries to attack the new kidney. This happens because:
- The transplanted kidney has different antigens on its surface
- Antigens are special proteins that act like identity tags
- The patient's immune system makes antibodies that see these antigens as foreign invaders
- These antibodies attack the transplanted kidney, causing rejection
The Rejection Challenge
Organ rejection is the body's natural immune response to foreign tissue. Even with the best medical care, there's always a risk that the patient's immune system will attack the transplanted kidney, potentially causing it to fail.
Preventing rejection
To stop the body rejecting the new kidney, doctors must:
- Match the antigens on the donor kidney as closely as possible to the patient's own antigens
- Give the patient immunosuppressant drugs for life to weaken their immune system
Critical Side Effect
Taking immunosuppressant drugs means the patient gets infections more easily than normal people. This is because the drugs that prevent rejection also make it harder for the body to fight off bacteria, viruses, and other harmful organisms.
Kidney dialysis
Kidney dialysis uses a special machine to do the job that healthy kidneys normally do. The machine philtres the patient's blood to remove waste products.
How dialysis works
The process works through diffusion:
- Blood flows from the patient through thin tubes in the dialysis machine
- These tubes are partially permeable - they let small molecules pass through but not big ones
- The tubes are surrounded by dialysis fluid
- Waste products like urea diffuse out of the blood into the dialysis fluid
- Clean blood flows back into the patient
Step-by-Step Dialysis Process
- Blood extraction: Blood is pumped from the patient's arm through a tube
- Filtration: Blood passes through partially permeable tubing surrounded by dialysis fluid
- Waste removal: Urea and other waste products diffuse across the membrane into the dialysis fluid
- Blood return: The cleaned blood flows back into the patient's body
- Waste disposal: Used dialysis fluid containing waste products is discarded
Why dialysis works so well
The dialysis system is cleverly designed:
- Dialysis tubing is partially permeable: This means blood cells, platelets and plasma proteins stay in the blood where they belong
- Dialysis fluid has no urea: This creates a concentration difference so urea diffuses out of the blood quickly
- Dialysis fluid contains useful substances: It has the same concentration of glucose and mineral ions as healthy blood, so these important substances don't get lost
Living with dialysis
Patients having dialysis must:
- Control the amount of protein in their diet to reduce urea production
- Attend hospital sessions that take several hours
- Have dialysis about three times per week
Life with Dialysis
Dialysis patients need to carefully plan their lives around treatment schedules. Each session typically lasts 3-4 hours, and missing sessions can be dangerous as waste products quickly build up in the blood.
Comparing the treatments
Kidney transplant advantages
- Patient can live a more normal life
- No need for regular hospital visits
- Can eat a normal diet
Kidney transplant disadvantages
- Donor kidneys are hard to find
- Risk of rejection
- Must take immunosuppressant drugs for life
- Risk of serious infections
Kidney dialysis advantages
- No need to find a donor
- No risk of rejection
- Treatment is always available
Kidney dialysis disadvantages
- Must visit hospital regularly
- Each session takes several hours
- Diet must be carefully controlled
- Less freedom and flexibility in daily life
Key Points to Remember:
- Kidney failure can be treated by transplant or dialysis
- Transplants give a more normal life but risk rejection and need immunosuppressant drugs
- Dialysis uses diffusion to philtre blood through partially permeable tubing
- Dialysis fluid has no urea but contains useful substances like glucose
- Both treatments have important advantages and disadvantages to consider