In the context of renal physiology, what effect does dilating the efferent arteriole have on the filtration fraction?

Dilating the efferent arteriole impacts the filtration fraction by reducing it. The filtration fraction is defined as the ratio of the glomerular filtration rate (GFR) to renal plasma flow (RPF). When the efferent arteriole is dilated, the resistance to blood flow out of the glomerulus decreases, which causes a drop in glomerular capillary hydrostatic pressure.

As the pressure within the glomerulus decreases, there is a subsequent reduction in GFR, as the driving force for filtration is compromised. While RPF may initially remain constant or even increase due to lower resistance, the larger effect tends to be the reduction in GFR in this scenario. Consequently, since the GFR falls while RPF may not change significantly, the filtration fraction decreases as a result.

This physiological concept is crucial for understanding renal hemodynamics and contributes to the broader knowledge of kidney function and its regulation.