Why does systemic vasodilation occur in severe allergic reactions involving ingested shellfish?

💡 Explanation

Severe allergic reactions (anaphylaxis) induce systemic vasodilation because ingested shellfish allergens trigger IgE-mediated mast cell degranulation, releasing large amounts of histamine. This potent vasodilator causes widespread vasodilation and subsequent drop in blood pressure; therefore, histamine release explains vasodilation, rather than complement activation or direct neurotransmitter effects.

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