Arteries are high-pressure blood vessels that carry oxygenated blood away from the heart to the tissues of the body, with the sole exception of the pulmonary arteries, which transport deoxygenated blood to the lungs. Structurally, they must withstand the powerful pulsatile force of ventricular contraction without bursting. As blood moves further away from the heart, arteries branch progressively into smaller vessels, dropping in size from large conducting vessels down to microscopic resistance vessels. This continuous branching network ensures every organ receives a steady supply of nutrients and oxygen necessary for cellular metabolism.
The wall of a typical artery consists of three distinct concentric layers, known as tunics.
Elastic arteries, also known as conducting arteries, include the aorta and its major initial branches. These large vessels possess thick walls packed with abundant sheets of elastin in the tunica media. When the left ventricle contracts, these massive arteries expand to absorb the sudden surge of blood volume. During ventricular relaxation, the stretched elastic fibers recoil passively, pushing the blood forward. This crucial dampening mechanism converts the harsh, intermittent pumping of the heart into a smoother, continuous flow by the time blood reaches smaller vessels.
Muscular arteries, or distributing arteries, deliver blood to specific body organs and feature a tunica media dominated by smooth muscle rather than elastic fibers. This abundance of muscle allows them to actively adjust the volume of blood delivered to different regions based on immediate metabolic needs. A baseline state of partial contraction, known as vasomotor tone, is maintained by the sympathetic nervous system. Increasing this tone causes vasoconstriction, while decreasing it results in vasodilation, directly shaping regional blood distribution throughout the body.
Arterioles are the smallest of the arterial vessels, possessing thin muscular walls that act as the primary control valves of the vascular system. Because of their tiny internal diameter, they create the most significant resistance to blood flow, earning them the label of resistance vessels. Small changes in the radius of an arteriole cause dramatic shifts in systemic blood pressure. By constricting or dilating, arterioles determine precisely how much blood enters capillary beds, protecting delicate downstream tissues from high pressure surges.
Blood movement through arteries is governed by basic fluid dynamics, where flow is directly proportional to the pressure gradient and inversely proportional to vascular resistance. Mean arterial pressure represents the average pressure driving blood through the systemic circulation, closely monitored by baroreceptors in the carotid sinuses and aortic arch. If blood pressure drops too low, neural and hormonal feedback loops prompt widespread vasoconstriction and increased heart rate. Conversely, chronic high pressure forces the heart to work harder, leading to potential cardiovascular strain over time.