Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What is the effect of the sympathetic nervous system on the lungs?

1. Stimulation of mucus production

2. Bronchial dilation

3. Bronchial constriction

4. Increased respiration rate

The correct answer is: Bronchial constriction

The effect of the sympathetic nervous system on the lungs is primarily characterized by bronchial dilation. This physiological response occurs during times of stress or increased physical activity when the body requires more oxygen. The sympathetic nervous system releases catecholamines, primarily epinephrine, which bind to beta-2 adrenergic receptors in the bronchial smooth muscle. This binding leads to relaxation of the bronchial smooth muscle and subsequent dilation of the airways, allowing for increased airflow into the lungs. In contrast to bronchial dilation, mucus production is generally inhibited by sympathetic stimulation, and the overall goal during sympathetic activation is to optimize respiratory function rather than reduce airway resistance. While an increased respiration rate can be part of the body's response to sympathetic activation, the direct effect on the bronchial smooth muscle is dilation rather than constriction. Thus, bronchial dilation is the correct characterization of sympathetic nervous system activity in the context of lung function.