<prompt> A 20 year old male patient came with the complaint of a decrease in the urinary output to about 400mlday. Both RBF and GFR were decreased. Which of the following causes a decrease in both RBF and GFR?Dilation of efferent aerioleDilation of afferent aerioleOnly afferent aeriolar constrictionOnly efferent aeriolar constriction  <response>: Constriction of either the afferent or efferent aeriole increases resistance, and according to Equation Q DPR, an increase in resistance R decreases flow Q i.e., RBF. Dilation of either the afferent or efferent aeriole increases flow i.e., RBF. Constriction of the afferent aeriole A decreases P GC because less of the aerial pressure is transmitted to the glomerulus, thereby reducing GFR. Dilation of the afferent aeriole increases P GC because more of the aerial pressure is transmitted to the glomerulus, thereby increasing GFR.Reference: Berne and Levy Medical Physiology; 6th edition; Page no: 574 