During a routine physiology experiment, a medical student measures the following values in a subject: glomerular capillary hydrostatic pressure = 55 mmHg, Bowman's space hydrostatic pressure = 15 mmHg, glomerular capillary oncotic pressure = 28 mmHg, and Bowman's space oncotic pressure = 0 mmHg. What is the net filtration pressure at the afferent end of the glomerular capillary?

• A 55 mmHg
• B 40 mmHg
• C 27 mmHg
• D 12 mmHg ✓

Explanation

Net filtration pressure = (PGC - PBC) - (πGC - πBC) = (55 - 15) - (28 - 0) = 40 - 28 = 12 mmHg. This is the standard Starling force calculation for glomerular filtration. Distractor C (27 mmHg) subtracts only oncotic pressure from Bowman's pressure. Distractor B (40 mmHg) ignores oncotic pressure entirely. Distractor A is simply the glomerular capillary pressure.

Reference: Boron and Boulpaep Medical Physiology, 3rd ed.

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