**Question:** Primary mediators of anaphylaxis are all EXCEPT:

A. Histamine
B. Bradykinin
C. Prostaglandins
D. Serotonin

**Core Concept:** Anaphylaxis is a severe, potentially life-threatening allergic reaction that involves the release of various mediators, including histamine, bradykinin, and serotonin. These mediators play a crucial role in the pathophysiology of anaphylaxis. Anaphylaxis is characterized by the rapid onset of systemic symptoms, such as hypotension, respiratory distress, and cardiovascular instability.

**Why the Correct Answer is Right:** C. Prostaglandins are not considered primary mediators of anaphylaxis because they are lipid-derived substances and do not directly originate from the mast cells or basophils, which are the primary cells involved in the early phase of anaphylaxis. Instead, they are involved in the late phase of anaphylaxis, contributing to bronchoconstriction, vasoconstriction, and increased vascular permeability.

**Why Each Wrong Option is Incorrect:**

A. Histamine is a primary mediator of anaphylaxis, released from activated mast cells and basophils, and contributes to the early phase symptoms.

B. Bradykinin is a secondary mediator, released from the degradation of kininogens by the enzyme kallikrein, and plays a role in the early phase by causing vasodilation, increased vascular permeability, and bronchoconstriction.

D. Serotonin is another primary mediator released from activated mast cells and basophils, contributing to the early phase symptoms of anaphylaxis.

**Clinical Pearl:**

Understanding the primary mediators of anaphylaxis is crucial for prompt and appropriate management. Early recognition and administration of epinephrine, a potent antagonist of histamine and bradykinin, plays a vital role in treating anaphylaxis.