A biological response that can cause swelling and narrowing of the airways in respiratory conditions.

• A. Bronchodilation
• B. Bronchoconstriction
• C. Inflammation
• D. Chemoreceptors

Answer: (C)

Swelling of the airway walls due to an inflammatory response is what narrows the airways in many respiratory conditions. When inflammation occurs, blood vessels in the airway lining become more permeable and dilate, causing edema (swelling). Immune cells migrate into the tissue and release mediators like histamine, leukotrienes, and cytokines. This sequence also stimulates mucus-producing glands and goblet cells, leading to extra mucus. The combination of swollen walls and increased mucus reduces the airway diameter, increasing resistance to airflow and making breathing more difficult.

Bronchodilation would widen the airways, not narrow them, so it doesn’t fit the description. Bronchoconstriction can narrow airways by tightening smooth muscle, but the question specifically emphasizes swelling, which points to an inflammatory process. Chemoreceptors are involved in detecting chemical changes to regulate breathing, not directly causing airway swelling or narrowing.