What is the primary role of the sympathetic nervous system in regard to bronchi?

The primary role of the sympathetic nervous system in relation to the bronchi is dilation to improve airflow. When the sympathetic nervous system is activated, it releases neurotransmitters such as norepinephrine, which bind to beta-2 adrenergic receptors located on the smooth muscle lining the bronchi. This binding causes the smooth muscles to relax, leading to the dilation of the bronchi. Increased diameter of the airways enhances airflow into the lungs, improving oxygen intake and facilitating breathing, especially during times of physical exertion or stress when the body requires more oxygen.

In contrast, the other options do not accurately reflect the primary actions of the sympathetic nervous system. Constriction of the bronchi would reduce airflow, which is contrary to the sympathetic system’s function in times of increased physical demand. Increased mucus production is typically more associated with the parasympathetic nervous system, which can enhance secretion during rest or digestion but compromises airflow. Lastly, decreasing blood supply doesn’t align with the sympathetic system’s role during fight-or-flight responses, where oxygen delivery to tissues, including those in the lungs, is prioritized.