Healthy kidneys filter the blood all day without our noticing. When they stop, wastes and water build up quickly, and the body needs outside help: a machine, the body's own membranes, or a new kidney. Sections 14.3.3 and 14.3.4 of the book describe all three.
Chapter 14 of the PECTAA Biology 12 book is the Human Urinary System. After urinary tract infections and kidney stones, the book covers kidney failure, dialysis and kidney transplant. This note is for FSc Part 2 (2nd year, Class 12) students in Lahore, Faisalabad, Sargodha, Rawalpindi, Multan, Gujranwala and the other Punjab boards. Gujrat district comes under the Gujranwala board. PECTAA writes the books. Your own board sets your paper.
What to know
Kidney (renal) failure (section 14.3.3). The kidneys lose their ability to filter wastes from the blood and to regulate fluid and salt balance.
- Chronic kidney failure: develops over a long period and is irreversible. Common causes are diabetes, high blood pressure and kidney disease such as chronic infection or inflammation of the glomeruli.
- Acute kidney failure (kidney injury): starts suddenly and often resolves with treatment. Causes include kidney infection; blockage of the urinary tract by kidney stones, bladder cancer or an enlarged prostate; some medicines such as NSAIDs; and blood clots in the renal arteries or arterioles.
Renal dialysis. Dialysis removes metabolic wastes from the blood by methods outside the normal working of the kidneys. There are two general types.
1. Haemodialysis.
- Blood is circulated outside the body through a dialyzer, a filter containing a semipermeable cellulose membrane.
- A catheter takes blood from an artery, usually in the arm, into the dialyzer.
- The dialyzer also holds a special fluid, the dialysate. Wastes, water and salts pass from the blood across the membrane into the dialysate.
- Clean blood returns to the body through a second catheter in a vein.
2. Peritoneal dialysis.
- Uses the peritoneal membrane that lines the abdominal cavity.
- 1.5 to 2 litres of dialysate is run into the abdomen through a catheter and left for 4 to 6 hours.
- Wastes and excess fluid pass from the blood capillaries of the peritoneum into the dialysate, which is then drained and discarded.
- The cycle is repeated several times a day.
Problems with dialysis.
- Access to the bloodstream raises the risk of infection.
- Low blood pressure (hypotension) is common in haemodialysis.
- Muscle cramps from changes in salt levels.
- Anaemia, causing tiredness and weakness.
- Removing too much fluid too fast can cause dehydration or low blood pressure.
- Emotional strain: patients may feel anxious, depressed or overwhelmed.
Kidney transplant (section 14.3.4). A surgical procedure that replaces a non-functioning kidney with a healthy one from a donor. It is offered to people with end-stage kidney failure and needs careful evaluation, matching and monitoring for both recipient and donor.
Potential donors.
- Related donor: a genetic relative such as a parent, sibling or child; the book calls this the best donor.
- Unrelated donor: someone not genetically related, such as a spouse, friend or co-worker. Less common, but it can succeed if blood group and tissue type match.
- Deceased donor: people who register to donate organs after death. Kidneys are matched by blood group, tissue type and immune compatibility.
Problems with transplant.
- Rejection: the immune system may attack the new kidney as foreign, even with immunosuppressant medicines.
- Infection: a suppressed immune system raises the risk.
- Side effects of immunosuppressants: high blood pressure, weight gain, and higher risk of infections and cancers.
Key points
- Chronic failure is irreversible; acute failure often recovers.
- Haemodialysis: dialyzer outside the body. Peritoneal: peritoneum inside the body.
- Dialysis works by passage of wastes across a semipermeable membrane into dialysate.
- Transplant success depends on matching blood group and tissue type.
Worked examples
Example 1 (classify the failure). A patient's kidneys stop working suddenly after a large stone blocks the ureter, and recover once it is removed.
- Sudden onset with recovery after treatment.
- This is acute kidney failure (kidney injury), caused by a urinary tract blockage.
Example 2 (peritoneal timing). Each exchange stays in the abdomen for 4 to 6 hours. How many full exchanges fit in 24 hours?
- 24 ÷ 6 = 4 and 24 ÷ 4 = 6.
- So between 4 and 6 dwell periods, which fits "several times a day".
Common mistakes in the exam
- Calling chronic failure reversible. The book says it is irreversible.
- Placing the dialyzer inside the body. In haemodialysis it is outside.
- Forgetting the membrane in peritoneal dialysis: it is the peritoneum.
- Thinking immunosuppressants remove all rejection risk. Rejection can still occur.
- Listing only medical problems of dialysis. The book also lists emotional strain.
Exam technique
- Compare the two dialysis types in a table: site, membrane, fluid, frequency.
- For transplant questions, give the three donor types first, then the three main problems, each with one line of explanation.
- Learn the causes of acute failure as a short list: infection, blockage, medicines, clots.
- Check your board's notice for the sections in your paper.
Practice questions
- Name the membrane used in a dialyzer. Answer: A semipermeable cellulose membrane.
- Give two causes of chronic kidney failure. Answer: Diabetes and high blood pressure.
- How much dialysate is used in one peritoneal exchange? Answer: 1.5 to 2 litres.
- Why is a parent often the best kidney donor? Answer: Genetic relatives are more likely to match in blood group and tissue type.
- State one side effect of immunosuppressant medicines. Answer: High blood pressure (also weight gain, or higher risk of infections and cancers).
Ready to practise this? Continue in 2nd Year Biology.