Which cell type forms the majority of the alveolar surface involved in gas exchange?

Which cell type forms the majority of the alveolar surface involved in gas exchange?

• A. Type II pneumocytes
• B. Bronchial epithelium
• C. Type I pneumocytes
• D. Alveolar macrophages

Answer: (C)

Gas exchange happens across a very thin barrier formed by Type I pneumocytes. These extremely flat, squamous cells line the majority of the alveolar surface—about 95%—and their thin cytoplasm minimizes the diffusion distance between the air in the alveoli and the blood in the surrounding capillaries, making O2 and CO2 exchange efficient. Type II pneumocytes are cuboidal and mainly responsible for producing surfactant to reduce surface tension; they cover a smaller portion of the surface but can proliferate to replace damaged Type I cells. Alveolar macrophages reside on the alveolar surface to clear debris and pathogens, not for gas exchange. Bronchial epithelium lines the conducting airways, not the alveolar spaces where gas exchange occurs.

Gas exchange happens across a very thin barrier formed by Type I pneumocytes. These extremely flat, squamous cells line the majority of the alveolar surface—about 95%—and their thin cytoplasm minimizes the diffusion distance between the air in the alveoli and the blood in the surrounding capillaries, making O2 and CO2 exchange efficient.

Type II pneumocytes are cuboidal and mainly responsible for producing surfactant to reduce surface tension; they cover a smaller portion of the surface but can proliferate to replace damaged Type I cells. Alveolar macrophages reside on the alveolar surface to clear debris and pathogens, not for gas exchange. Bronchial epithelium lines the conducting airways, not the alveolar spaces where gas exchange occurs.