If the afferent arteriole of the nephron constricts, what happens to the GFR in that nephron? If the efferent arteriole constricts what happens to the GFR in that nephron? Assume that no auto regulation takes place.

Explanation

Constriction of either the afferent or afferent arterioles can alter the glomercular hydrostatic pressure. Constriction of the afferent arterioles has two affects . It increases the vascular resistance which reduces the renal blood flow and it decreases the pressure down stream from the constriction which reduces GFR
Constriction of efferent arterioles also increases the vascular resistance so it reduces the RBF (Renal blood flow). The pressure within the glomerular capillaries may increase, however, because the flow is slowed by efferent arteriolar constriction.