This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Physiology
Which of the following is not an effect of efferent aeriole constriction : 
Select and explain. 
A. Decreased GFR, B. Increased glomerular hydrostatic pressure, C. Decreased blood flow in peritubular vessels, D. Increased oncotic pressure in peritubular vessels
A: Decreased GFR
Answer: A: Decreased GFR 
Explanation: 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.