Health Issues Related to the Urinary System
Common urinary system health issues include kidney stones, which block the flow of urine, and kidney failure, in which the kidneys can no longer filter blood properly, requiring treatment by dialysis or a kidney transplant.
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Kidney stones
Kidney stones are hard deposits, usually of crystallised mineral salts such as calcium salts, that form inside the kidney when substances in urine become too concentrated. A stone can block a ureter as it passes through, causing severe pain and sometimes blood in the urine; larger stones may need to be broken up or removed medically.
Drinking enough water to keep urine dilute lowers the risk of stones forming.
Kidney failure
Kidney failure occurs when the kidneys can no longer filter blood adequately, so urea and other waste products, along with excess water and salts, build up in the blood instead of being removed as urine. It can result from long-term conditions such as diabetes and high blood pressure, from infection, or from direct damage to the kidneys, and if untreated it can become life-threatening as toxic waste accumulates in the body.
Treating kidney failure
| Treatment | How it works | Consideration |
|---|---|---|
| Dialysis | A machine (or the lining of the abdomen, in peritoneal dialysis) filters urea and excess substances out of the blood across a partially permeable membrane outside the body | Needs to be repeated regularly, often several times a week, and does not cure the underlying kidney damage |
| Kidney transplant | A healthy kidney from a donor is surgically placed in the body to take over normal filtering function | Restores more normal function with a single healthy kidney, but the patient must take immunosuppressant medication for life to prevent the body rejecting it |
How it is examined
Questions on this standard often ask you to identify or explain the cause of a described urinary health problem, to compare the advantages and disadvantages of dialysis and a kidney transplant, or to suggest a lifestyle measure, such as adequate water intake, that reduces the risk of kidney stones.
Worked exam-style question
Question. A patient with long-term untreated high blood pressure is diagnosed with kidney failure. Blood tests show a build-up of urea in her blood.
She begins haemodialysis treatment three times a week. (a) Explain, in terms of the nephron, why her kidneys can no longer remove urea effectively.
(b) Explain how haemodialysis removes urea from her blood. (c) State one disadvantage of haemodialysis compared with a kidney transplant.
Model answer. (a) Long-term high blood pressure damages the tiny blood vessels and nephrons within the kidney, impairing ultrafiltration, the process by which the nephron normally filters urea and other wastes out of the blood, so urea builds up in the blood instead of being removed as urine. (b) In haemodialysis, blood is passed across a partially permeable membrane outside the body, allowing urea and excess substances to diffuse out of the blood into the dialysis fluid, in the same way a healthy kidney would remove them.
(c) Haemodialysis must be repeated regularly (often several times a week) for the rest of her life unless she receives a transplant, whereas a transplant restores more normal kidney function with a single procedure.
Practice question
Try this. A man who drinks very little water throughout the day develops sudden, severe pain in his side, and a scan reveals a hard deposit blocking part of his ureter. Explain how his low water intake is linked to this condition, and suggest how he could reduce his risk of it happening again.
Exam tip
Key terms
These terms from Chapter 13 support this topic:
- Nephron, the microscopic filtering unit of the kidney, damaged in kidney failure.
- Ultrafiltration, the process in the nephron that filters small molecules, including urea, out of the blood under pressure.
- Osmoregulation, the control of water and salt balance in the body, which the kidney also carries out.
- Deamination, the removal of the amino group from excess amino acids in the liver, producing the urea that the kidney later removes.
Source:SRC-DSKP-EN
Frequently asked questions
What causes kidney stones, and how can the risk be reduced?
How does dialysis compensate for kidney failure?
Why does kidney failure cause urea to build up in the blood specifically?
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