What role does the parasympathetic nervous system play in respiration?

• A. It dilates airways
• B. It constricts airways
• C. It stabilizes breathing rate
• D. It increases oxygen absorption

Answer: (B)

The parasympathetic nervous system is primarily responsible for the body's rest-and-digest functions. In the context of respiration, its activation leads to the constriction of airways. This occurs due to the release of acetylcholine, which acts on muscarinic receptors in the bronchial smooth muscle, causing it to contract. As a result, the airway diameter decreases, making it easier to handle normal, relaxed breathing, especially during periods of calm. This constriction serves as a contrast to the sympathetic nervous system, which is activated in times of stress or exertion and causes bronchial dilation to facilitate increased airflow.

Understanding this function is crucial for appreciating how the autonomic nervous system regulates respiratory mechanics, allowing the body to optimize breathing according to varying levels of activity and relaxation.