Microscopic anatomy of an artery.
Cross-section of a human artery
The anatomy of arteries can be separated into gross anatomy, at the macroscopic level, and microanatomy, which must be studied with a microscope. The arterial system of the human body is divided into systemic arteries, carrying blood from the heart to the whole body, and pulmonary arteries, carrying deoxygenated blood from the heart to the lungs.
The outermost layer of an artery (or vein) is known as the tunica externa, also known as tunica adventitia, and is composed of collagen fibers and elastic tissue - with the largest arteries containing vasa vasorum (small blood vessels that supply large blood vessels). Inside this layer is the tunica media, or media, which is made up of smooth muscle cells, elastic tissue (also called connective tissue proper) and collagen fibres. The innermost layer, which is in direct contact with the flow of blood, is the tunica intima, commonly called the intima. The elastic tissue allows the artery to bend and fit through places in the body. This layer is mainly made up of endothelial cells (and a supporting layer of elastin rich collagen in elastic arteries). The hollow internal cavity in which the blood flows is called the lumen.
Arterial formation begins and ends when endothelial cells begin to express arterial specific genes, such as ephrin B2.