Squamous epithelial cells are flat cells that are usually arranged in a thin, single layer. Due to its thickness, the exchange of the gases into and out of the lungs through simple diffusion* is easier to happen. Gas molecules like oxygen and carbon dioxide easily diffuse because these are small, non-polar molecules.
*Short diffusion pathway = a simple diffusion through a single layer of cells. Example: Exchange of gas in and out of the squamous epithelial cells of the lungs
