What role does smooth muscle play in the bronchioles?

Smooth muscle in the bronchioles plays a crucial role in regulating airflow by controlling the diameter of these airways. The contraction and relaxation of smooth muscle fibers allow for the adjustment of the bronchioles' size, which directly influences the amount of air that can pass through during respiration. When the smooth muscle contracts, the diameter of the bronchioles decreases, leading to reduced airflow — an important mechanism during situations like asthma, where bronchoconstriction occurs. Conversely, when the smooth muscle relaxes, the bronchioles widen, allowing for increased airflow, which is vital during physical exertion when higher oxygen demands are present. Thus, the primary function of smooth muscle in this context is to regulate the airflow by altering the diameter of the bronchioles, facilitating efficient gas exchange in the lungs.