Final answer:
The alveoli of the lungs are comprised of epithelial tissue, more specifically, a simple squamous epithelium that facilitates efficient gas exchange due to its thin structure and the extensive surface area provided by the numerous alveoli.
Step-by-step explanation:
The alveoli of the lungs are comprised of epithelial tissue. Specifically, the alveoli are lined with a simple squamous epithelium formed by type I alveolar cells, which are connected to a thin, elastic basement membrane. This epithelial layer borders the endothelial membrane of the capillaries and together they form the respiratory membrane. The respiratory membrane's structure is critical, being approximately 0.5 μm thick, which facilitates the gas exchange process via simple diffusion.
With oxygen entering the blood and carbon dioxide being expelled into the air of the alveoli, this exchange allows the respiratory system to function efficiently. Moreover, the vast number of alveoli, with the two lungs containing approximately 700 million, provide an extensive surface area equivalent to half a tennis court for effective gas exchange.