Which tissue type lines the alveoli and capillaries to facilitate gas exchange?

Which tissue type lines the alveoli and capillaries to facilitate gas exchange?

• A. Stratified squamous epithelium
• B. Simple cuboidal epithelium
• C. Simple squamous epithelium
• D. Pseudostratified columnar epithelium

Answer: (C)

Gas exchange relies on a very thin barrier so oxygen and carbon dioxide can diffuse quickly between air and blood. The lining of the alveoli is made up of simple squamous epithelial cells (type I pneumocytes), and the surrounding capillaries are lined with simple squamous endothelial cells. Because both sides are single, flat cell layers, the respiratory membrane becomes extremely thin, promoting efficient diffusion. Other tissue types are thicker or structured for protection or secretion rather than facilitating gas diffusion: stratified squamous is multi-layered and protective, simple cuboidal is thicker and found in glands and kidney tubules, and pseudostratified columnar lines much of the airway but isn’t the thin diffusion surface of the alveoli.

Gas exchange relies on a very thin barrier so oxygen and carbon dioxide can diffuse quickly between air and blood. The lining of the alveoli is made up of simple squamous epithelial cells (type I pneumocytes), and the surrounding capillaries are lined with simple squamous endothelial cells. Because both sides are single, flat cell layers, the respiratory membrane becomes extremely thin, promoting efficient diffusion. Other tissue types are thicker or structured for protection or secretion rather than facilitating gas diffusion: stratified squamous is multi-layered and protective, simple cuboidal is thicker and found in glands and kidney tubules, and pseudostratified columnar lines much of the airway but isn’t the thin diffusion surface of the alveoli.