During anaphylaxis, how does histamine affect bronchial smooth muscle?

During anaphylaxis, how does histamine affect bronchial smooth muscle?

• A. constricts
• B. relaxes
• C. no effect
• D. dilates

Answer: (A)

Histamine released during anaphylaxis binds to H1 receptors on bronchial smooth muscle, increasing intracellular calcium and triggering muscle contraction. This causes bronchoconstriction, narrowing the airways and raising airway resistance, which explains the wheeze and shortness of breath seen in anaphylaxis. Histamine’s actions in the airways promote constriction rather than relaxation or dilation, and while it also increases airway mucosal edema and mucus production, the immediate effect on the bronchi is constriction.

Histamine released during anaphylaxis binds to H1 receptors on bronchial smooth muscle, increasing intracellular calcium and triggering muscle contraction. This causes bronchoconstriction, narrowing the airways and raising airway resistance, which explains the wheeze and shortness of breath seen in anaphylaxis. Histamine’s actions in the airways promote constriction rather than relaxation or dilation, and while it also increases airway mucosal edema and mucus production, the immediate effect on the bronchi is constriction.