Which tissue type lines the alveoli, enabling rapid diffusion of gases across the surface?

Which tissue type lines the alveoli, enabling rapid diffusion of gases across the surface?

• A. Endothelium of blood vessel
• B. Pseudostratified ciliated columnar epithelium
• C. Simple cuboidal epithelium
• D. Simple squamous epithelium

Answer: (D)

Gas exchange requires a very thin, permeable surface, so the alveoli are lined with simple squamous epithelium. The flat, single-cell-thick layer minimizes diffusion distance, allowing oxygen to move quickly from the air into the blood and carbon dioxide to diffuse out. The other tissues don’t provide that ultra-thin surface: the endothelium lines blood vessels, not the air-filled sacs; pseudostratified ciliated columnar epithelium lines most of the respiratory tract and helps move mucus; simple cuboidal epithelium lines many ducts and tubules but isn’t the thin surface used for gas diffusion.

Gas exchange requires a very thin, permeable surface, so the alveoli are lined with simple squamous epithelium. The flat, single-cell-thick layer minimizes diffusion distance, allowing oxygen to move quickly from the air into the blood and carbon dioxide to diffuse out. The other tissues don’t provide that ultra-thin surface: the endothelium lines blood vessels, not the air-filled sacs; pseudostratified ciliated columnar epithelium lines most of the respiratory tract and helps move mucus; simple cuboidal epithelium lines many ducts and tubules but isn’t the thin surface used for gas diffusion.