What causes bronchoconstriction in the airways?

Bronchoconstriction primarily occurs when the smooth muscle surrounding the airways contracts, leading to a narrowing of the larger airways such as the bronchi and bronchioles. This contraction can result from various stimuli, including allergens, irritants, and certain medications, causing the airways to become constricted and reducing airflow.

While inflammation of the tissue can contribute to bronchoconstriction by worsening the condition of the airways, the direct mechanism of bronchoconstriction is specifically the action of the smooth muscle. Excess mucus production can further obstruct airflow, but the primary cause of the narrowing effect is indeed the contraction of the smooth muscle. Finally, increased air pressure does not directly cause bronchoconstriction; rather, it may influence airflow dynamics in other ways unrelated to the contraction of bronchial smooth muscle. Therefore, the correct answer focuses on the role of smooth muscle in narrowing the airways.