This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood: Hemostasis and Blood Coagulation, Subject name: Physiology
Flare response in triple response occurs due to- 
Select and explain. 
A. Vasodilation due to release of secondary mediators, B. Chemotaxis, adhesion of leucocytes to vessel wall, C. Direct vessel injury, D. Increased permeability
A: Vasodilation due to release of secondary mediators
Answer: A: Vasodilation due to release of secondary mediators 
Explanation: Ans. is 4a' i.e., Vasodilation due to release of secondary mediatorsTriple responseo When a pointed object is stroked very firmly over the skin, a characteristic 3 part response develops. Its feature are-1) Red reaction {red line) is due to transient capillary engorgement (vasodilation) caused by histamine released from damaged tissue. Histamine relaxes precapillary sphincter thus leads to capillary dilatation.2) Flush or flare is spreading of redness beyond the injury (red line). It is due to arteriolar dilation mediated by axon reflex (may be an indirect effect of histamine).3) Wheal is local edema and elevation of skin due to increased permeability of capillaries and post capillary venules with consequent extravasation of fluid. Capillary permeability' is increased due to histamine and other mediators.