This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Triple response is due to ? 
Select and explain. 
A. Serotonin, B. Histamine, C. Dopamine, D. Bradykine
B: Histamine
Answer: B: Histamine 
Explanation: Ans. is 'b' i.e., Histamine Triple response (Lewis triple response) When a pointed object is stroked very firmly over the skin, a characteristic 3 pa 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 aeriolar 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.