Simple squamous epithelium

Consists of polyhedral cells which are flattened. They can be either dissociated or compact epithelium. They line the inside of blood vessels and the heart where they are called endothelium. They are also found in alveolar sacs and they line the inside of abdominal and pleural cavities and are called mesothelium in these locations. They are also found in the loop of Henle in the kidney. They usually serve protective function.