Which cells produce surfactant in the alveoli?

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

Answer: (A)

Surfactant is produced by Type II pneumocytes, the cuboidal cells embedded in the alveolar walls. These cells synthesize phospholipids and specific surfactant proteins, store them in lamellar bodies, and release them into the alveolar lining. The surfactant lowers surface tension at the air–liquid interface, preventing collapse of the tiny alveoli during expiration and helping keep gas exchange efficient. The other cell types have different roles: Type I pneumocytes cover most of the alveolar surface to facilitate diffusion, alveolar macrophages defend against pathogens and debris, and Clara (Club) cells reside in bronchioles and secrete protective substances there rather than in the alveoli.