The simple squamous epithelium is a single layer of flat, scale-like cells that rests on a basement membrane. These cells are thin and smooth, providing a low-friction surface ideal for rapid diffusion and filtration of molecules across the membrane. It is often called pavement epithelium because the cells look like floor tiles when viewed from the top. This epithelium is avascular, tightly packed with little space between cells, and contains membrane proteins that help transfer ions, gases, and small molecules. There are two main types:

• The endothelium, which lines blood vessels, the heart, and lymphatic vessels, facilitating the quick exchange of substances.
• The mesothelium, which lines serous membranes such as the peritoneum, secreting lubricating fluids for smooth organ movement.

Functions include protection (against mild trauma and toxins), absorption and transportation (via diffusion, osmosis, and filtration), and secretion (of lubricants like mucus). Locations include alveoli in the lungs, blood vessel linings, kidney structures such as the Bowman’s capsule, and body cavity linings like the peritoneum. In summary, simple squamous epithelium serves as a delicate, efficient barrier for exchange of gases, fluids, and nutrients while providing some protection and secretion roles in the body.