Source / episode info

• **Episode:**54
• **Title:**Divine Intervention Episode 54 – Comprehensive USMLE Step 1 Renal Review (Session 3 of 3).
• **Published:**2018-09-28
• Source:Episode page

One-liner

This comprehensive renal review covers tubular physiology (diuretics, hormones), electrolyte imbalances (hyponatremia workup), the pathophysiology and management of nephrolithiasis, and key aspects of kidney development and cystic disease (ADPKD).

High-yield summary

• Hyponatremia Workup: The diagnosis depends on volume status: Hypovolemic -> Low UNa; Hypervolemic -> High UNa; Euvolemic -> Variable/SIADH.
• Pseudo-hyponatremia: Occurs when high levels of non-sodium solutes (e.g., glucose in DKA, immunoglobulins) artificially dilute the measured sodium concentration.
• ADPKD: Associated with renal failure, intracranial aneurysms (Circle of Willis), and cardiac disease; PKD1 is more strongly associated with early renal failure.
• Nephrolithiasis: Calcium oxalate stones are common in Crohn's disease due to fat malabsorption leading to increased oxalate absorption. Uric acid stones precipitate in acidic urine/acidosis. Struvite stones are infection-related (alkaline).
• Hormonal Action: PTH increases renal synthesis of active Vitamin D (1-hydroxylase) and stimulates calcium reabsorption via the DCT. Aldosterone acts on principal cells to increase {Na}^+ reabsorption.

Learning objectives

• Differentiate the causes of hyponatremia based on volume status (hypovolemic, euvolemic, hypervolemic).
• Identify the specific metabolic or GI conditions that lead to nephrolithiasis formation (e.g., Crohn's -> oxalate; Acidosis -> uric acid).
• Recognize the clinical manifestations and genetic basis of ADPKD and ARPKD.
• Describe the hormonal regulation of sodium, potassium, and calcium reabsorption in the distal nephron.
• Interpret laboratory findings (e.g., urine osmolality, free water clearance) to diagnose fluid/electrolyte imbalances.

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