Overview
Each kidney contains about a million nephrons. In each nephron, blood is filtered in the glomerulus, then the tubules reabsorb what the body needs (water, glucose, sodium, bicarbonate) and secrete what it does not (hydrogen ions, potassium, drugs).
Urine flows from the renal pelvis down the ureters to the bladder, which stores it until urination through the urethra. The female urethra is short (about 4 cm), which is why urinary tract infections are more common in women.
Main functions
- Filtering waste such as urea and creatinine from the blood
- Regulating fluid volume and blood pressure (renin–angiotensin–aldosterone system)
- Balancing sodium, potassium, calcium and other electrolytes
- Maintaining acid–base balance by excreting H+ and reabsorbing bicarbonate
- Producing erythropoietin for red blood cell production
- Activating vitamin D
Key structures
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Kidneys
Two bean-shaped organs that filter the blood and make urine.
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Ureters
Two narrow muscular tubes that carry urine from the kidneys to the bladder.
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Urinary bladder
A stretchy muscular reservoir in the pelvis that stores urine.
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Urethra
The tube that carries urine from the bladder out of the body.
Inside the nephron
Blood enters the glomerulus through the afferent arteriole. Pressure pushes water and small solutes into Bowman's capsule; cells and large proteins stay in the blood, so protein or blood in the urine signals glomerular damage. The glomerular filtration rate (GFR) is normally about 90–120 mL/min.
The proximal tubule reabsorbs most of the filtrate. The loop of Henle concentrates urine (loop diuretics act here). In the distal tubule and collecting duct, aldosterone saves sodium and excretes potassium, and ADH saves water.
Nursing assessment
- Measure intake and output; adult urine output should be at least 30 mL/hour (0.5 mL/kg/hour).
- Weigh daily at the same time, with the same scale and clothing: 1 kg equals about 1 L of fluid.
- Inspect urine color, clarity and odor; ask about frequency, urgency, dysuria and hematuria.
- Percuss the costovertebral angle (CVA): tenderness suggests kidney infection.
- Palpate or scan the bladder for distension and retention.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Urinary tract infection | Bacterial infection of the bladder (cystitis) or kidney (pyelonephritis) | Dysuria, frequency, urgency; flank pain and fever with pyelonephritis; confusion in older adults | Clean-catch specimen before antibiotics, fluids, teach front-to-back wiping and voiding after intercourse |
| Acute kidney injury | Sudden loss of kidney function (prerenal, intrarenal or postrenal) | Oliguria, rising creatinine and BUN, fluid overload, hyperkalemia | Strict I&O, daily weights, monitor potassium and ECG, avoid nephrotoxic drugs |
| Chronic kidney disease | Progressive, irreversible loss of nephrons | Fatigue, edema, hypertension, anemia, itching, uremic breath | Fluid, sodium, potassium and phosphorus restriction; protect the fistula arm; medication adjustments |
| Kidney stones | Mineral stones in the urinary tract | Severe colicky flank pain radiating to the groin, hematuria, nausea | Pain control, fluids, strain all urine, save stones for analysis |
| Benign prostatic hyperplasia | Enlarged prostate narrows the urethra | Weak stream, hesitancy, nocturia, retention | Bladder scan, catheter if retention, monitor after TURP for bleeding and clots |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| Serum creatinine | About 0.6–1.2 mg/dL (lower in women) | The best routine indicator of kidney function |
| BUN | 10–20 mg/dL | Also rises with dehydration, GI bleeding and high protein intake |
| eGFR | 90 mL/min/1.73 m² or higher | Below 60 for 3 months indicates chronic kidney disease |
| Potassium | 3.5–5.0 mEq/L | Rises in kidney failure; above 6.0 can cause fatal dysrhythmias |
| Urine specific gravity | 1.005–1.030 | High when concentrated (dehydration), low when diluted |
| Urinalysis: protein, glucose, nitrites, leukocyte esterase | Negative | Nitrites and leukocyte esterase suggest infection |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- Less than 30 mL/hour of urine for 2 consecutive hours in an adult must be reported.
- Never take blood pressure, draw blood or start an IV in the arm with a dialysis fistula; feel the thrill and listen for the bruit.
- Hyperkalemia shows on the ECG as tall peaked T waves.
Practice questions
8 NCLEX-style questions on the urinary system. Pick an answer to see the rationale.
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Which urine output should the nurse report for an adult client?
Show the answer and rationale
Answer B: 25 mL/hour for 2 hours. Output below 30 mL/hour (0.5 mL/kg/hour) suggests poor kidney perfusion or acute kidney injury.
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A client's potassium is 6.4 mEq/L. Which ECG change does the nurse expect?
Show the answer and rationale
Answer B: Tall peaked T waves. Hyperkalemia produces tall peaked T waves and can progress to dangerous dysrhythmias.
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Which lab value is the best routine indicator of kidney function?
Show the answer and rationale
Answer B: Serum creatinine. Creatinine depends mostly on kidney filtration. BUN is also affected by hydration, protein intake and GI bleeding.
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A client has an arteriovenous fistula in the left arm for dialysis. Which action is correct?
Show the answer and rationale
Answer C: Palpate for a thrill and auscultate for a bruit. A thrill and bruit confirm the fistula is patent. Never use that arm for blood pressure, IVs or blood draws.
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Which teaching helps prevent urinary tract infections in women?
Show the answer and rationale
Answer C: Void after intercourse. Voiding after intercourse flushes bacteria from the urethra. Wiping front to back and good fluid intake also help.
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Severe flank pain radiating to the groin with hematuria suggests:
Show the answer and rationale
Answer B: Kidney stone. A stone moving down the ureter causes colicky pain radiating to the groin and blood in the urine.
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Where are the kidneys located?
Show the answer and rationale
Answer B: Retroperitoneal, around T12–L3. The kidneys lie behind the peritoneum on each side of the spine, the right slightly lower.
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Which hormone causes the kidneys to reabsorb water?
Show the answer and rationale
Answer B: ADH (antidiuretic hormone). ADH makes the collecting ducts permeable to water. Aldosterone reabsorbs sodium, with water following.