Parasympathetic stimulation of the lungs produces which combination of effects?

• A. Bronchodilation, Vasoconstriction, and glandular secretion
• B. Bronchodilation and Vasoconstriction
• C. Bronchoconstriction only
• D. Bronchodilation and Vasodilation

Answer: (C)

Parasympathetic input to the lungs, carried by the vagus nerve, releases acetylcholine that acts on muscarinic receptors in the airway. The dominant effect on the bronchial smooth muscle is contraction mediated by M3 receptors, which narrows the airways (bronchoconstriction). It also increases glandular secretions in the airway mucosa, but the airway-caliber change is the most direct and characteristic result. Among the given options, bronchoconstriction is the primary and most consistent effect of parasympathetic stimulation on the lungs, while the other choices describe responses (bronchodilation or vascular changes) that are not produced by parasympathetic activation.