Which of the following describes the effect of sympathetic stimulation on the bronchi?

• A. Bronchodilation
• B. Bronchoconstriction
• C. No change
• D. Increased mucus production

Answer: (A)

When the sympathetic nervous system is active, airway smooth muscle relaxes and the bronchi widen, a process called bronchodilation. This happens because adrenaline-like signals bind to beta-2 adrenergic receptors on the airway smooth muscle, triggering a cascade that increases cAMP and causes the muscles to relax. The result is a larger airway lumen and easier breathing—why beta-2 agonist drugs like albuterol are used to treat bronchospasm.

Bronchoconstriction would occur with parasympathetic activity (and certain inflammatory mediators), narrowing the airways, not widening them. No change isn’t correct because there is a clear, physiologically consistent effect. Increased mucus production isn’t driven by sympathetic stimulation; mucus secretion is more associated with parasympathetic input and inflammatory processes.