Increase in renal blood flow increases GFR. Afferent aeriole brings blood to the nephron hence its dilation will increase renal blood flow, and efferent aeriole takes blood away from the nephrons, hence its constriction will cause increase filtration, hence increase in GFR. Constriction of afferent aeriole: decreases both renal blood flow and GFR, without change in filtration fraction. Dilatation of afferent aeriole : increases both renal blood flow and GFR, without change in filtration fraction. Constriction of efferent aeriole: decreases the renal blood flow and increases GFR and filtration fraction. Dilatation of efferent aeriole: increases the renal blood flow and decreases the GFR and filtration fraction.