What physiological changes occur during an allergic reaction?

The correct answer highlights the important role of histamines and the process of vasodilation that occurs during an allergic reaction. When an individual is exposed to an allergen, the immune system reacts by producing immunoglobulin E (IgE) antibodies specific to that allergen. This triggers mast cells and basophils to release histamines, which are key mediators in allergic responses.

Histamine acts on various target cells in the body and causes vasodilation, which is the widening of blood vessels. This action increases blood flow to the affected areas, leading to redness and swelling, common symptoms of allergic reactions. Additionally, histamines increase the permeability of blood vessels, allowing fluid to leak into the surrounding tissues, which can result in hives, itching, and other typical allergic symptoms.

In summary, during an allergic reaction, the release of histamines is crucial in mediating symptoms through vasodilation and increased vascular permeability, contributing significantly to the body's inflammatory response. This physiological response is essential for addressing the allergen but can lead to the symptoms that characterize allergic reactions when the response is excessive or inappropriate.