The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. Endothelial cells form the barrier between vessels and tissue and control the flow of substances and fluid into and out of a tissue.
Transmission electron micrograph of a microvessel showing endothelial cells, which encircle an erythrocyte (E), forming the innermost layer of the vessel, the tunica intima.
Endothelium lines the inner wall of vessels, shown here.
Epithelium or epithelial tissue is a thin, continuous, protective layer of compactly packed cells with little extracellular matrix. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. These tissues also lack blood or lymph supply. The tissue is supplied by nerves.
Types of epithelium
Summary showing different epithelial cells/tissues and their characteristics.
Different characteristics of glands of the body
Epithelial cell infected with Chlamydia pneumoniae