What happens to the smooth muscle in the airways during exhalation?

During exhalation, the smooth muscle in the airways constricts to help push air out of the lungs. This process is referred to as airway constriction or bronchoconstriction. When the smooth muscles around the bronchi and bronchioles contract, they narrow the air passages, which increases the pressure in the airways and assists in expelling the air from the lungs. This action is important for maintaining proper airflow and can be affected by various factors such as exercise, allergens, and environmental irritants.

In contrast, airways that remain relaxed would not effectively facilitate exhalation, and expansion of the smooth muscle would lead to increased airway diameter, which is not conducive to pushing air out. Additionally, the generation of mucus is a separate function that occurs in response to irritants or allergens, serving primarily to protect and moisten the airways rather than directly assisting in the mechanics of exhalation. Therefore, the contraction of the smooth muscles during exhalation plays a crucial role in the respiratory process.