Overview
This lecture reviews essential nephrology concepts for the USMLE and shelf exams, focusing on kidney physiology, acute and chronic kidney diseases, glomerular and tubular disorders, renal stones, and urologic conditions.
Renal Physiology & Acute Kidney Injury
- Kidneys receive 20% of cardiac output but filter only 120 mL/min (GFR).
- Pre-renal AKI: low urine sodium (<20), high urine osmolality, hyaline casts, BUN/Cr ratio >20:1, treated with fluids.
- Intrinsic AKI/ATN: high urine sodium, muddy (epithelial cell) casts, recover in 2-3 weeks, often drug-induced (aminoglycosides, contrast).
- Acute interstitial nephritis: white blood cell casts, often drug-induced (penicillins, NSAIDs), treat by stopping the drug, sometimes steroids.
Glomerular Diseases & Nephrotic/Nephritic Syndromes
- Nephrotic syndrome: proteinuria >3.5g/day, hypoalbuminemia, hyperlipidemia, edema, increased risk of thrombosis/infections.
- Nephritic syndrome: hematuria, red cell casts, hypertension, mild proteinuria.
- Post-streptococcal GN: low C3, periorbital edema, follows strep infection.
- IgA nephropathy: hematuria, normal complement.
- Membranous nephropathy: check for Hep B/C, SLE, malignancy.
Renal Tubular Disorders & Electrolytes
- Renal tubular acidosis Type 4 causes hyperkalemia.
- Hyperkalemia: peaked T waves, treat urgently with calcium gluconate.
- Thiazides can cause hypokalemia, hyponatremia.
- Gitelman syndrome mimics chronic thiazide use; Bartter/Liddle—different tubule segments.
- Rapid correction of hyponatremia can cause osmotic demyelination.
Renal Stones
- Calcium oxalate: most common, Crohn’s disease risk, treat with thiazides.
- Uric acid stones: radiolucent, treat with urine alkalinization (potassium citrate).
- Struvite: staghorn calculi, Proteus/Klebsiella.
- Stones <5mm: hydration, strain urine; 5-10mm: tamsulosin; >10mm: surgery.
Chronic Kidney Disease & Complications
- CKD leads to anemia, bone disease (secondary hyperparathyroidism), hyperkalemia, easy bruising.
- Polycystic kidney disease: presents in 30s-40s, associated with cerebral aneurysm, hypertension.
Urologic & Other Renal Disorders
- BPH: tamsulosin/terazosin (alpha blockers), finasteride (5-ARI), TURP if severe.
- Testicular torsion: emergency, Doppler US, surgery within 6 hours.
- Urinary incontinence: stress—Kegel exercises; urge—oxybutynin; overflow—bethanechol.
- Pediatric UTIs: treat for E. coli, consider ultrasound for anatomic anomalies.
Key Terms & Definitions
- GFR — Glomerular filtration rate, amount of plasma filtered by kidneys per minute.
- AKI — Acute kidney injury, sudden decline in renal function.
- Nephrotic Syndrome — Kidney disorder with high proteinuria, low albumin, edema, hyperlipidemia.
- Nephritic Syndrome — Kidney inflammation with hematuria, red cell casts, variable proteinuria.
- Cast — Cylindrical particles in urine indicating kidney pathology.
- Tamsulosin — Alpha-blocker for stone passage and BPH.
- Kegel Exercises — Pelvic floor muscle exercises for stress incontinence.
Action Items / Next Steps
- Review chart/lab features of AKI types.
- Memorize nephrotic vs. nephritic syndrome criteria.
- Practice differentiating renal tubular disorders.
- Study renal stone types, treatment, and imaging findings.
- Know first-line treatments for common urologic complaints.
- Review recommended readings or textbook chapters as assigned.