Arteries are blood vessels that transport oxygenated blood from the heart to other organs and systems throughout the body. In humans, healthy arteries are smooth, elastic structures, while diseased arteries may contain bulges due to high blood pressure, hard, inelastic areas, or internal blockages resulting from the accumulation of fatty plaques circulating in the blood. Atherosclerosis is the hardening or narrowing of an artery after plaque formation has partially restricted blood flow through the artery. Atherosclerosis is the major contributor to coronary artery disease (CAD), and coronary artery disease, often resulting in heart attack or arrhythmia, is the number one cause of deaths in the United States.
In humans, a typical artery contains an elastic arterial wall that can be divided into three principal layers, although the absolute and relative thickness of each layer varies with the type or diameter of artery. The outer layer is termed the tunica adventia, the middle layer is termed the tunica media, and an inner layer is the tunica intima. These layers surround a lumen, or opening, that varies in size with the particular artery, through which blood passes.
Arteries of varying size comprise a greater arterial blood system that includes, in descending diameter, the aorta, major arteries, smaller arteries, arterioles, meta-arterioles, and capillaries. It is only at the level of the capillary that branches of arteries become thin enough to permit gas and nutrient exchange. As the arterial system progresses toward the smaller diameter capillaries, there is a general and corresponding increase in the number of branches and total area of lumen available for blood flow. As a result, the rate of flow slows as blood approaches the capillary beds. This slowing is an important feature that enables efficient exchange of gases—especially oxygen.
In larger arteries, the outer, middle, and inner endothelial and muscle layers are supported by elastic fibers, and serve to channel the high pressure and high rate of blood flow. A difference in the orientation of cells within the layers (e.g., the outer endothelial cells are oriented longitudinally, while the middle layer smooth muscle cells run in a circumference around the lumen) also contributes both strength and elasticity to arterial structure.
The aorta and major arties are highly elastic, and contain walls with high amounts of elastin. During heart systole (contraction of the heart ventricles), the arterial walls expand to accommodate the increased blood flow. Correspondingly, the vessels contract during diastole and this contraction also serves to drive blood through the arterial system.
In the systemic arterial network that supplies oxygenated blood to the body, aortas are regions of the large-lumened singular artery arising from the left ventricle of the heart. Starting with the ascending aorta that arises from the left ventricle, the aortas form the main trunk of the systemic arterial system. Before the ascending aorta curves into the aortic arch, right and left coronary arteries branch off to supply the heart with oxygenated blood. Before the aortic arch turns to continue downward (inferiorly) as the descending aorta, it gives rise to a number of important arteries. Branching either directly off of—or from a trunk communicating with the aortic arch—is a brachiocephalic trunk that branches into the right subclavian and right common carotid artery that supply oxygenated blood to the right sight of the head and neck, as well as portions of the right arm.
The aortic arch also gives rise to the left common carotid artery that, along with the right common carotid artery, branches into the external and internal carotid arteries to supply oxygenated blood to the head, neck, brain.
The left subclavian artery branches from the aortic arch and—with the right subclavian arising from the brachiocephalic trunk—supplies blood to neck, chest (thoracic wall), central nervous system, and arms via axillary, brachial, and vertebral arteries.
In the chest (thoracic region), the continuation of the aortic arch—the descending aorta—is specifically referred to as the thoracic aorta. The thoracic aorta is the trunk of arterial blood supply to the thoracic region. As the thoracic aorta passes through an opening in the diaphragm (aortic hiatus) to become the abdominal aorta, parietal and visceral branches supply oxygenated blood to abdominal organs and structures. The abdominal aorta ultimately branches into left and right common iliac arteries that then branch into internal and external iliac arteries, supplying oxygenated blood to the organs and tissues of the lower abdomen, pelvis, and legs.