Arteries are the blood vessels that carry blood away from the heart. Every artery in your body, from the massive aorta down to the tiniest branch, moves blood outward from one of the heart’s two lower chambers (ventricles). Veins do the opposite, returning blood back to the heart.
How Arteries Move Blood From the Heart
Your heart has two separate pumping sides, and each one sends blood into a major artery. The left ventricle pushes oxygen-rich blood into the aorta, the largest artery in the body, which then distributes it to every organ and tissue. The right ventricle pushes oxygen-poor blood into the pulmonary artery, which routes it to the lungs to pick up a fresh supply of oxygen.
This distinction matters because arteries don’t always carry oxygen-rich blood. The pulmonary arteries are a notable exception: they carry blood away from the heart just like all other arteries, but that blood is low in oxygen and headed to the lungs. So the defining feature of an artery isn’t its oxygen content. It’s the direction of flow: away from the heart.
The Aorta and Its Major Branches
The aorta is the main highway of the arterial system. It attaches directly to the left ventricle and curves upward, arches over the top of the heart, then runs straight down through the chest and abdomen. It has four main sections: the aortic root (where it connects to the heart), the ascending aorta (the upward curve), the aortic arch (the bend at the top), and the descending aorta (the long straight portion running through the torso).
From these sections, branches split off to supply different parts of the body. The coronary arteries branch off almost immediately, right near the root, and wrap around the outside of the heart to feed the heart muscle itself. The aortic arch sends branches up toward the brain, head, neck, and arms. Further down, the descending aorta branches to supply the organs of the chest and abdomen, eventually splitting into arteries that serve the legs.
Why Artery Walls Are Built Differently Than Veins
Arteries need to withstand a lot more pressure than veins. Each time your heart beats, it generates a surge of force that pushes blood into the arterial system. A healthy blood pressure reading is less than 120/80 mm Hg, and that pressure is measured specifically inside arteries. Veins, by comparison, operate under much lower pressure.
To handle this, artery walls are built with three distinct layers. The innermost layer is a smooth lining that lets blood flow with minimal friction. The middle layer is the thickest, made primarily of muscle tissue. This muscular wall gives arteries their strength and, more importantly, the ability to widen or narrow to control how much blood flows through. The outer layer is tough connective tissue that anchors the artery to surrounding structures and provides additional support.
Veins have these same three layers, but their walls are thinner and less muscular. Because blood in veins is under low pressure, many veins contain one-way valves to prevent blood from flowing backward. Arteries don’t need valves because the heart’s pumping force keeps blood moving in the right direction.
From Large Arteries to Tiny Arterioles
Arteries don’t stay large. They branch repeatedly, getting progressively smaller the farther they travel from the heart. The smallest arteries, called arterioles, are where your body does most of its fine-tuning of blood flow and blood pressure.
Arterioles have muscular walls that can constrict or relax in response to signals from the surrounding tissue. When an organ needs more oxygen (during exercise, for example), the cells around its arterioles release chemical signals that cause those tiny vessels to widen, increasing blood flow to meet the demand. Your nervous system also plays a role: it keeps arterioles partially constricted at baseline, maintaining steady blood pressure throughout the body. Hormones circulating in the blood, like adrenaline, can further tighten or relax these vessels depending on what your body needs in the moment.
Eventually, arterioles branch into capillaries, the smallest blood vessels in the body. Capillaries are where the actual exchange of oxygen, nutrients, and waste happens between blood and tissue. After passing through capillaries, blood enters tiny veins and begins its return trip to the heart.
The Coronary Arteries: Feeding the Heart Itself
The heart is a muscle, and like every other muscle it needs its own blood supply. The coronary arteries handle this job. Two main coronary arteries branch off the aorta right where it leaves the heart, then wrap around the heart’s surface.
The left main coronary artery supplies the left side of the heart and splits into two important branches: one sends blood to the front of the heart and the wall dividing the two ventricles, while the other circles around to feed the outer side and back. The right coronary artery supplies the right side of the heart, including the nodes that control your heart rhythm. Because the heart never stops working, these arteries are critically important. A blockage in any of them can starve part of the heart muscle of oxygen, which is what happens during a heart attack.
What Happens When Arteries Get Blocked
The most common threat to arteries is a gradual buildup of plaque along their inner walls, a process called atherosclerosis. It starts when fats and cholesterol accumulate beneath the artery’s smooth inner lining, forming small deposits. Over time, immune cells invade these deposits, and the fatty material breaks down into a soft, unstable core covered by a fibrous cap.
As plaque grows, it narrows the artery and restricts blood flow. Organs downstream receive less oxygen than they need, which can cause symptoms like chest pain (when coronary arteries are affected) or leg pain during walking (when arteries in the legs narrow). The more dangerous scenario occurs if the fibrous cap over a plaque ruptures. The exposed material inside triggers a blood clot that can suddenly block the artery entirely, cutting off blood flow to whatever tissue it supplies.
The Pulse You Feel Is an Arterial Event
When you press your fingers to your wrist or neck and feel a pulse, you’re feeling the pressure wave generated by your heartbeat traveling through an artery. Each contraction of the left ventricle sends a surge of blood into the aorta, and that surge ripples outward through the arterial tree as a wave of pressure.
The speed of this pulse wave is actually a useful indicator of arterial health. In healthy, flexible arteries, the wave travels at a moderate pace. As arteries stiffen with age or disease, the wave moves faster and bounces back more quickly, which places extra strain on the heart. Pulse wave velocity is now considered a gold-standard noninvasive measure of arterial stiffness.