Infusion of a modest dose of angiotensin II constricts the efferent arteriole more than the afferent. What are the expected immediate effects on glomerular capillary hydrostatic pressure and filtration fraction?

• A Both decrease
• B Glomerular pressure rises and filtration fraction falls
• C Glomerular pressure falls and filtration fraction rises
• D Glomerular pressure rises and filtration fraction rises ✓

Explanation

Constricting the efferent arteriole raises resistance downstream of the glomerulus, so glomerular capillary hydrostatic pressure rises and GFR tends to increase. Because renal plasma flow falls sharply while GFR rises or holds steady, filtration fraction, defined as GFR divided by renal plasma flow, clearly increases. Only severe efferent constriction reverses the GFR change by slowing peritubular capillary flow and raising colloid osmotic pressure enough to oppose filtration. Angiotensin II also constricts mesangial cells, but at modest doses the efferent effect dominates the measured outcome.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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