Which of the following is not an effect of efferent aeriole constriction :
(A) Decreased GFR (B) Increased glomerular hydrostatic pressure (C) Decreased blood flow in peritubular vessels (D) Increased oncotic pressure in peritubular vessels
(A) Constriction of efferent aeriole has biphasic effect on GFR. At moderate levels of constriction, It increases glomerular hydrostatic pressure resulting in increasing GFR If efferent aeriolar constriction is severe; It decreases renal blood flow; filtration fraction & glomerular colloid osmotic pressure increases as efferent aeriolar resistance increases resulting in colloid osmotic pressure exceeds increase in glomerular capillary hydrostatic pressure resulting in decrease in GFR. Blood from efferent aerioles enter peritubular capillaries, so if efferent aeriole is constricted, less blood enters peritubular capillaries, which results in increase in oncotic pressure in peri tubular capillaries.