Lewis Triple Response is mediated by:
**Core Concept**
The Lewis triple response is a physiological response to injury, characterized by a triad of increased blood flow (redness), edema (swelling), and a blister-like lesion (wheal). It is a local inflammatory response to histamine release from mast cells.
**Why the Correct Answer is Right**
The Lewis triple response is primarily mediated by histamine, a chemical mediator released from mast cells in response to injury. Histamine causes vasodilation (widening of blood vessels), increased permeability of capillaries, and smooth muscle contraction, leading to the characteristic redness, swelling, and blister-like lesion. The response is also modulated by other chemical mediators, such as bradykinin and serotonin, but histamine is the primary mediator.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the vasodilation and increased permeability of capillaries are due to histamine, not acetylcholine.
**Option B:** This option is incorrect because the Lewis triple response is a local inflammatory response, not a systemic response mediated by the hypothalamus.
**Option C:** This option is incorrect because the response is primarily histamine-mediated, not due to the release of other chemical mediators such as bradykinin and serotonin.
**Clinical Pearl / High-Yield Fact**
The Lewis triple response is an example of a local inflammatory response, which can be seen in conditions such as allergic reactions, insect bites, and contact dermatitis.
**Correct Answer: D. Histamine. Histamine**