thus, a drop in blood pressure results in preferential vasodilation of the afferent arterioles, increasing renal blood flow (rbf), renal plasma flow (rpf) and gfr due to greater blood flow to the glomerulus. note that there is no change in filtration fraction, as both gfr and rpf are increased. it also results in the release of renin, which, through the renin–angiotensin system, causes constriction of the efferent arterioles, which ultimately increases hydrostatic pressure in the glomerulus.