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 connective tissue made up of collagen fibers. Inside this layer is the tunica media, or media, which is made up of smooth muscle cells and elastic tissue (also called connective tissue proper). The innermost layer, which is in direct contact with the flow of blood, is the tunica intima, commonly called the intima. This layer is mainly made up of endothelial cells. 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.