Parasympathetic activity in the lungs leads to which of the following?

• A. Bronchodilation and Vasodilation
• B. Bronchodilation only
• C. Bronchoconstriction, Vasodilation, and Glandular Secretion
• D. Bronchodilation and Glandular Secretion

Answer: (C)

Parasympathetic input to the lungs is carried by the vagus nerve and uses acetylcholine to act on muscarinic receptors, mainly M3, in three key sites: airway smooth muscle, submucosal glands, and the pulmonary endothelium. When acetylcholine binds to M3 receptors on airway smooth muscle, it causes contraction, leading to bronchoconstriction. On the glands, the same signaling increases mucus and other glandular secretions. In the pulmonary vasculature, acetylcholine can stimulate the endothelium to release nitric oxide, which relaxes vascular smooth muscle and causes vasodilation. Putting these together, parasympathetic activity produces bronchoconstriction, vasodilation, and glandular secretion.