Efficient exchange of gases in the air sacs of the lungs occur due to the presence of

Simple squamous epithelial cells are thin and flat (the thinnest of all epithelial cell-types). They form the diffusion and filtration membranes. Due to their simple and thin structure, they allow for easy transmembrane movement of small molecules. Molecules such as oxygen and carbon dioxide diffuse freely across the simple squamous epithelia according to concentration gradients.