A 55-year-old man with long-standing hypertension develops nephrosclerosis. His inulin clearance is measured at 60 mL/min. If renal plasma flow is 500 mL/min and filtration fraction increases compared to normal, which of the following best explains the change in filtration fraction?

• A Increased hydrostatic pressure in Bowman's space
• B Decreased oncotic pressure in peritubular capillaries
• C Preferential efferent arteriolar constriction by angiotensin II ✓
• D Reduced filtration coefficient (Kf) due to mesangial cell contraction

Explanation

Angiotensin II preferentially constricts the efferent arteriole, maintaining GFR when renal perfusion drops. This raises glomerular capillary hydrostatic pressure and filtration fraction. Increased Bowman's space pressure would reduce GFF. Reduced Kf would lower both GFR and filtration fraction.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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