Final answer:
Sympathetic fibers in the respiratory system innervate the lungs, bronchial tree, trachea, and larynx, aiding in the regulation of airflow by causing bronchodilation.
Step-by-step explanation:
In the respiratory system, sympathetic fibers innervate various structures to control airway resistance and regulate airflow. These structures include the lungs, bronchial tree, trachea, and the fourth option provided, the larynx. The sympathetic nervous system promotes bronchodilation to enhance airflow, in contrast to the parasympathetic nervous system which causes bronchoconstriction. Both systems play crucial roles in the function of the respiratory system, including the ability to cough and regulate the levels of oxygen and carbon dioxide in the blood. The sympathetic fibers align with the airways, allowing for this precise control over respiratory functions.