What are the functions of simple squamous epithelium?

The simple squamous epithelium is mono-layered and composed of thin, flattened squamous cells. It is found lining the organs of the cardiovascular and lymphatic systems, the alveoli of the lungs, and the intestine among others. Depending on its location, the simple squamous epithelium may have many different functions.  

• Simple squamous epithelium present in the lining of blood vessels and air sacs enables the easy exchange of gases and other molecules between tissues. 
• Simple squamous epithelium found in kidney glomeruli and air sacs of the lungs allows for efficient filtration of substances while preventing large molecules from passing through.
• Although the simple squamous epithelium is the most delicate type of epithelium in the body, it provides an effective barrier against harmful substances, as seen in the lining of the heart and blood vessels.
• It also provides protection to underlying tissues against toxins, invasion by foreign invaders, and desiccation. 
• The simple squamous epithelium in the serous membranes lining body cavities secretes lubricating substances to create a smooth, frictionless surface. 

Overall, simple squamous epithelium's thin and flat structure is well-suited for allowing rapid exchange and movement of substances across surfaces.