FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Blood vessel structure. Artwork showing the layers of tissue in the walls of a vein. In the lumen of the vein are valves (grey) that prevent the back flow of blood. The inner layer (tunica intima) of the vessel is composed of endothelium (pink). This is surrounded by a thin layer of smooth muscle, the tunica media (orange). The outer layer is a sheath of connective tissue known as the tunica adventita (blue).
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