simple squamous epithelium is a single layer of flat scale-shaped cells. Both the endothelial lining of blood vessels and the mesothelial lining of the body cavities are simple squamous epithelium. found in lining the cavities of the body including the pericardial, pleural, and peritoneal cavities, or in areas where passive diffusion occurs, such as glomeruli in the kidney and alveoli in the respiratory tract.