Which statement best describes cystic fibrosis?

• A. Decreased mucus production
• B. Airway obstruction due to smooth muscle hyperplasia
• C. Chronic productive cough with mucous plugging
• D. Thick mucus that impairs gas exchange

Answer: (D)

Cystic fibrosis stems from defective CFTR chloride channels, which reduces chloride and water movement on mucosal surfaces. This leaves secretions abnormally thick and sticky, making mucus difficult to clear from the airways. That thick mucus tends to plug airways, causing obstruction and recurrent infections, and most importantly it impairs gas exchange by creating ventilation–perfusion mismatch and potential hypoxemia. Among the statements, thick mucus that impairs gas exchange best describes the core functional consequence of the disease. Decreased mucus production isn’t correct, since the problem is mucus is too thick, not too little. Airway obstruction due to smooth muscle hyperplasia isn’t the primary driver in CF, and while a chronic productive cough with mucus plugging is common, the fundamental description is the impact of thick mucus on gas exchange.