In the early phase of histamine exposure, the primary effect on the airways is which of the following?

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Multiple Choice

In the early phase of histamine exposure, the primary effect on the airways is which of the following?

Histamine’s immediate effect in the airways is to contract bronchial smooth muscle. It binds to H1 receptors on the muscle lining the airways, triggering a signaling cascade that raises intracellular calcium and prompts the smooth muscle to squeeze the airways shut a bit. This bronchoconstriction happens within minutes of exposure and is the primary early-phase change in airway function. Other effects histamine can cause—like vasodilation of surrounding vessels or mucus production and eosinophil recruitment—occur but are not the main early event in the airways. Eosinophil recruitment and mucus hypersecretion are more characteristic of the later, sustained inflammatory phase.

Histamine’s immediate effect in the airways is to contract bronchial smooth muscle. It binds to H1 receptors on the muscle lining the airways, triggering a signaling cascade that raises intracellular calcium and prompts the smooth muscle to squeeze the airways shut a bit. This bronchoconstriction happens within minutes of exposure and is the primary early-phase change in airway function.

Other effects histamine can cause—like vasodilation of surrounding vessels or mucus production and eosinophil recruitment—occur but are not the main early event in the airways. Eosinophil recruitment and mucus hypersecretion are more characteristic of the later, sustained inflammatory phase.

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