[HAP-05] Renal Anatomy, Nephron Filtration, Tubular Transport, RAAS & Fluid–Electrolyte Balance

HAP-05 • 1. Anatomy & Physiology

Learning Objectives

Trace glomerular filtration (GFR ~125 mL/min, Starling forces, afferent prostaglandin PGE2 dilation vs efferent Angiotensin II constriction).; Map tubular reabsorption across the PCT (65% Na+, 100% glucose via SGLT2/1), Loop of Henle (25% Na+ via NKCC2), DCT (5–10% Na+ via NCC), and Collecting Duct (ENaC & Aquaporin-2).; Explain the 'Triple Whammy' acute kidney injury (NSAID + ACEi/ARB + Diuretic) and Cockcroft–Gault renal dose adjustment.

Chapter Overview & Core Explanation

Each kidney contains about one million microscopic filtering units called nephrons. Together they filter 180 litres of plasma every day, reclaiming essential glucose, amino acids, and electrolytes while excreting urea, creatinine, and water-soluble drugs.

Key Exam & Clinical Takeaways

• Prostaglandins (PGE2/PGI2) dilate the afferent arteriole, whereas Angiotensin II preferentially constricts the efferent arteriole to preserve GFR.
• SGLT2 inhibitors ([7.7] Dapagliflozin, [7.8] Empagliflozin) restore tubuloglomerular feedback by increasing Na+ delivery to the macula densa, reducing glomerular hyperfiltration and slowing CKD progression.

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