Question

A person is given a drug that dilates the afferent arterioles and constricts the efferent arterioles of their nephrons. Assuming no other actions of the drug, how will the Starling forces influencing filtration across the glomerulus be affected?

Answer 1

RBF will show no change because the drug has no effect on total renal vascular resistance. GFR will increase because of a large increase in P(GC). Filtration fraction will, therefore, increase. (Now back up and think a bit more about the GFR: Because filtration fraction increases, there will be a larger than average increase in π(GC) along the glomeruli, and this will offset some of the GFR-increasing effects of the increased P(GC); therefor, GFR will not increase as much proportionately as the P(GC).