Triple response is due to -

Ans. is 'b' i.e.. Histamine Triple response (Lewis triple response)o When a pointed object is stroked very firmly over the skin, a characteristic 3 part response develops. Its feature are :-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.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). 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.