Which physiological change occurs during an acute allergic reaction?

During an acute allergic reaction, the immediate release of histamines is a key physiological change. Histamines are chemical messengers released by mast cells and basophils in response to an allergen, which is a substance that triggers an allergic reaction. When an allergen enters the body, it binds to immunoglobulin E (IgE) antibodies on the surface of these cells, leading to their degranulation and the rapid release of histamines into the bloodstream.

The release of histamines causes various symptoms, such as vasodilation, increased permeability of blood vessels, and stimulation of gastric acid secretion. These actions contribute to the characteristic manifestations of an allergic reaction, including swelling, redness, itching, and potentially more severe outcomes like anaphylaxis. Understanding this mechanism is crucial for recognizing and managing allergic reactions effectively.

The other options involve physiological processes that do not occur as a direct and immediate response to an allergen. While increased production of antibodies can happen over time with repeated exposure to an allergen, it is not an immediate response in the acute phase. Declined blood circulation to extremities typically does not occur in acute allergic reactions; instead, patients may experience swelling and increased blood flow in response to histamines. Heightened production of red