Blood vessel between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart. The word "vascular", meaning relating to the blood vessels, is derived from the Latin "vas", meaning vessel. A few structures (such as cartilage and the lens of the eye) do not contain blood vessels and are labeled. The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins: Capillaries consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of
Coronary arteries Coronary arteries The coronary arteries are the arteries of the coronary circulation, which transports blood into and out of the cardiac muscle. They are mainly composed of the left and right coronary arteries, both of which give off branches. Coronary arteries can also be categorized as Epicardial (above the epicardium) and Microvascular (close to the endocardium). The left coronary artery arises from the aorta above the left cusp of the aortic valve and feeds blood to the left side of the heart. It branches into two arteries and sometimes a third branch is formed at the fork, known as a