Disorders of the Excretory System: Kidney Failure, Stones

The excretory system filters blood in the kidneys and removes waste as urine. When its parts fail or become blocked, waste and fluid collect in the body. Common disorders include kidney failure, kidney stones, infections and glomerulonephritis.

These disorders matter because untreated kidney failure is life-threatening. Early signs can be silent, so blood tests, urine tests and blood pressure control are important, especially in people with diabetes and high blood pressure, the two leading causes of chronic kidney disease.

Key Concepts

• Uremia: Accumulation of urea and other wastes in blood due to kidney failure, causing nausea, confusion and breathlessness.
• Acute kidney failure: Sudden loss of kidney function over hours to days, sometimes reversible if the cause is treated.
• Chronic kidney disease: Gradual, usually permanent loss of function over months to years.
• Kidney stones (renal calculi): Hard crystals, often calcium oxalate, formed in the kidney or urinary tract that can block urine flow.
• Glomerulonephritis: Inflammation of glomeruli that lets protein and blood leak into urine.
• Dialysis: Artificial filtering of blood when kidneys cannot do it adequately.

How It Works

1. Healthy nephrons filter about 180 litres of fluid daily and reabsorb most of it, producing 1 to 2 litres of urine.
2. In chronic disease, nephrons are progressively destroyed by high blood sugar, high pressure, inflammation or obstruction. Remaining nephrons overwork and also fail.
3. As filtration falls, urea, creatinine, potassium and acids rise in blood, while fluid retention raises blood pressure and causes swelling.
4. Stones form when urine is concentrated or rich in calcium, oxalate or uric acid. A stone moving into the ureter causes severe colicky pain, vomiting and sometimes blood in urine.
5. Infection by bacteria, usually from the urethra upward, causes burning urination, fever and urgency; untreated infection can reach the kidneys.

Worked Example

Normal glomerular filtration rate (GFR) is about 125 millilitres per minute in a young adult. Daily filtration = 125 × 60 × 24 = 180,000 millilitres = 180 litres per day. If GFR falls to 15 millilitres per minute in severe failure, daily filtration = 15 × 60 × 24 = 21,600 millilitres = 21.6 litres, showing why waste clearance becomes inadequate even though some filtration remains. Such patients often need dialysis or transplantation.

Common Misconceptions

• Back pain always means kidney disease: Wrong. Most back pain is muscular; kidney disease often has no pain until late.
• Less urine is the only sign: Wrong. Some patients pass normal urine volume but fail to remove wastes properly.
• Stones are caused only by eating calcium: Wrong. Low water intake and several metabolic factors matter; dietary advice depends on stone type.

Real-World Applications

Serum creatinine and estimated GFR stage kidney disease. Ultrasound detects stones and obstruction. Treatment includes controlling diabetes and pressure, low-salt diet, medicines, stone removal by lithotripsy or surgery, and dialysis or transplant in end-stage disease. Drinking adequate water helps prevent many stones.

In summary, excretory disorders range from painful stones to silent chronic failure. Protecting the kidneys through early testing and risk-factor control can delay or prevent dialysis.