Which alveolar cell type is primarily responsible for surfactant production?

• A. Type 1 pneumocytes
• B. Type 2 pneumocytes
• C. Alveolar macrophages
• D. Endothelial cells

Answer: (B)

Surfactant production in the alveoli comes from Type II pneumocytes. These cuboidal alveolar cells contain lamellar bodies that store surfactant lipids and proteins. They synthesize key components, including phospholipids like dipalmitoylphosphatidylcholine and surfactant proteins, and then secrete them into the alveolar space. The surfactant film lowers surface tension at the air-liquid interface, preventing alveolar collapse during exhalation and helping keep the lungs open. Additionally, Type II cells can proliferate and differentiate into Type I cells after injury to help regenerate the alveolar lining. By contrast, Type I pneumocytes are the thin cells that form the majority of the gas-exchange surface but do not produce surfactant, alveolar macrophages are responsible for immune defense and debris clearance, and endothelial cells line the capillaries in the alveolar walls but do not produce surfactant.