Squamous epithelium forms a selectively permeable surface at the lining of blood vessels.
Epithelial tissue is classified based on the cell shape and the number of cell layers.
- Cell shape: squamous, cuboidal, columnar
- Cell layers: simple (one layer), stratified (multiple layers).
This type of epithelial lines the inner surface of all blood vessels (endothelium), forms the wall of alveolar sacs in the lung and lines the body cavities (mesothelium). The primary function of simple squamous epithelia is to facilitate the diffusion of gases and small molecules. Squamous epithelial cells appear squashed or flattened, like flakes or fish scales. The cells are wider than they are tall, with an oval-shaped nucleus.