Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What is the outcome of the parasympathetic nervous system on lung motility?

1. Increased bronchial tone

2. Decreased lung capacity

3. Bronchial dilation

4. Bronchial constriction

The correct answer is: Increased bronchial tone

The outcome of the parasympathetic nervous system on lung motility primarily results in increased bronchial tone. This is achieved through the release of acetylcholine from parasympathetic nerves, which binds to muscarinic receptors on the bronchial smooth muscles. This interaction causes the smooth muscles to contract, leading to bronchoconstriction. Increased bronchial tone is essential for regulating airflow and is particularly beneficial during times of rest and digestion, where a more relaxed state is advantageous. While bronchial constriction may inherently imply increased tone, referring to it specifically as "increased bronchial tone" emphasizes the ongoing physiological state as opposed to just the act of constricting. This can help in understanding conditions like asthma, where parasympathetic hyperactivity can lead to excessive bronchoconstriction and decreased airflow. It is important to note that bronchial dilation, which might occur under the influence of the sympathetic nervous system, contrasts with the effects of the parasympathetic nervous system and is mediated by different mechanisms involving adrenergic receptors. Similarly, decreased lung capacity would not directly stem from the actions of the parasympathetic system but rather from a combination of factors affecting lung function, including but not limited to bronchial tone.