What does the squamous (flattened) epithelial cell do?

The squamous cell epithelium forms a barrier between the body and the exterior environment. The cells also provide protection for the underlying tissues

Squamous epithelial cells are flat and are usually found lining surfaces that require a smooth flow of fluid such as your blood vessels, or lining areas that require a very thin surface for molecules to pass through, such as the air sacs in your lungs.