Which cells synthesize and secrete pulmonary surfactant to reduce alveolar surface tension?

• A. Type I pneumocytes
• B. Alveolar macrophages
• C. Type II pneumocytes
• D. Clara cells

Answer: (C)

Pulmonary surfactant is produced by specialized alveolar cells called type II pneumocytes. These cells store surfactant in lamellar bodies and secrete phospholipids (primarily DPPC) along with specific surfactant proteins that line the alveolar surface. This coating lowers surface tension at the air–liquid interface inside the alveoli, preventing collapse during expiration and increasing lung compliance.

Type I pneumocytes line most of the alveolar surface and handle gas exchange, but they do not synthesize surfactant. Alveolar macrophages reside in the air spaces to clear debris and pathogens, not to produce surfactant. Clara cells, located in the bronchioles, secrete protective substances and participate in detoxification, but they do not synthesize pulmonary surfactant.