Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

Which system's effect leads to bronchial dilation in the lungs?

1. Parasympathetic nervous system

2. Sympathetic nervous system

3. Central nervous system

4. Peripheral nervous system

The correct answer is: Sympathetic nervous system

The sympathetic nervous system is responsible for bronchial dilation in the lungs. This dilation occurs as part of the "fight or flight" response, where the body prepares for increased physical activity. When the sympathetic nervous system is activated, it releases catecholamines, such as epinephrine and norepinephrine, which bind to beta-2 adrenergic receptors located in the bronchial smooth muscle. This binding results in relaxation of the smooth muscles in the airways, leading to dilation and an increased airflow into the lungs. In contrast, the parasympathetic nervous system typically causes bronchoconstriction, promoting airway narrowing. The central nervous system does play a role in regulating respiratory function, but it does not directly cause bronchial dilation. Lastly, while the peripheral nervous system encompasses both the sympathetic and parasympathetic systems, it is the specific activation of the sympathetic system that is directly responsible for the dilation of the bronchi. Therefore, the sympathetic nervous system's actions are crucial for facilitating airflow during times of increased demand.