PATHOLOGY

Detailed explanation-1: -Histamine is a major preformed mediator released by mast cells and it strongly increases vascular permeability. This increase in vascular permeability is responsible for several features of acute allergic reactions including edema, urticaria, and anaphylactic shock in serious cases.

Detailed explanation-2: -Conclusions: Histamine can produce vasodilation of submucosal arterioles by two distinct mechanisms: activation of vascular H1 receptors resulting in release of nitric oxide from endothelium and activation of H3 receptors on sympathetic nerve terminals resulting in presynaptic inhibition of vasoconstrictor tone.

Detailed explanation-3: -One of the best-known chemical mediators released from cells during inflammation is histamine, which triggers vasodilation and increases vascular permeability.

Detailed explanation-4: -Histamine increases the vasodilatation, and also increases the vascular permeability in the immediate transient phase of the acute inflammatory reaction. This act as a chemical mediator in acute inflammation. Keywords-Vasoactive amine, vasodilatation, chemical mediator, mast cells.