What is the primary cause of hypotension in anaphylactic shock?

The primary cause of hypotension in anaphylactic shock is indeed related to the over-exaggeration of the immune response. In anaphylaxis, the body encounters an allergen that triggers a dramatic immune reaction, leading to the release of a large amount of histamine and other inflammatory mediators.

Histamine causes vasodilation, which is the widening of blood vessels, and increases the permeability of the blood vessel walls. This reaction results in a significant decrease in vascular resistance and an increase in fluid leakage from the bloodstream into the surrounding tissues. The overall effect is a drop in blood pressure, or hypotension, as the circulating blood volume is effectively reduced, and the vascular system becomes less effective at maintaining adequate blood pressure.

While decreased blood volume and inadequate intravascular fluid may be contributing factors, they are not the primary cause. In anaphylactic shock, it’s the severe immune response and consequent vasodilation that primarily drive the hypotension.