Arteries carry blood away from the heart. Every time your heart beats, it pushes blood into these strong, muscular vessels, which then deliver it to every organ and tissue in your body. The two main arteries leaving the heart are the aorta, which sends oxygen-rich blood to your body, and the pulmonary artery, which sends oxygen-poor blood to your lungs. From there, the arterial system branches into progressively smaller vessels until blood reaches the tiny capillaries where oxygen and nutrients are actually exchanged.
The Two Major Arteries Leaving the Heart
Your heart has two ventricles, and each one pumps blood into its own major artery. The left ventricle, the most powerful chamber, generates the high pressure needed to push blood into the aorta. The aorta is the largest artery in your body, about 3 to 4 centimeters wide and roughly 2 to 3 inches long in just its first ascending section. From there it arches and branches downward, feeding oxygen-rich blood into a vast network that reaches your brain, arms, organs, and legs. This network is called the systemic circuit.
The right ventricle pumps blood into the pulmonary artery, which leads to your lungs. This is an important exception to the common rule that arteries carry oxygen-rich blood. The pulmonary arteries are the only arteries in your body that carry oxygen-poor blood. Their job is to route blood to the lungs so it can pick up fresh oxygen and release carbon dioxide. Once that exchange happens, the blood returns to the left side of the heart through pulmonary veins, ready to be pumped out through the aorta again.
Why Arteries Are Built Differently Than Veins
Arteries need to handle a lot of force. Each heartbeat creates a surge of pressure, and arterial walls are specifically designed to absorb it. They have three distinct layers. The innermost layer is a smooth lining that lets blood flow with minimal friction. The middle layer is the thickest, packed with smooth muscle cells and elastic fibers that allow the artery to stretch with each pulse and then snap back. The outer layer contains connective tissue, nerve endings, and tiny blood vessels that supply the artery wall itself.
Veins have the same three layers, but with significantly less smooth muscle and connective tissue. That makes vein walls thinner and more flexible. The difference comes down to pressure: blood in arteries is under much higher pressure than blood in veins, so arteries need thicker, more rigid walls. Veins, by contrast, are floppy enough to hold larger volumes of blood at low pressure, which is why they serve as a reservoir for your circulatory system.
How Arteries Keep Blood Flowing Between Heartbeats
Your heart doesn’t push blood in a continuous stream. It pumps in bursts, one squeeze at a time. Yet blood flows through your body in a relatively steady manner. Arteries make this possible through their elasticity. When the heart contracts, large arteries like the aorta stretch outward to absorb the surge of blood. When the heart relaxes between beats, the arterial walls recoil inward, pushing blood forward. This creates a smoothing effect, converting a pulsing output into more continuous flow through your smaller vessels.
This is why you can feel a pulse at your wrist or neck. That rhythmic throb is the arterial wall expanding and contracting with each heartbeat. Normal blood pressure, the force that blood exerts against arterial walls, is below 120/80 mmHg. When pressure stays elevated at 130/80 or higher, it’s classified as hypertension, which over time can damage the elastic fibers in artery walls and make them stiffer.
From Arteries to Arterioles to Capillaries
Arteries don’t deliver blood directly to your cells. They branch into smaller and smaller vessels, eventually becoming arterioles, which are the final step before capillaries. Arterioles are tiny but powerful regulators of blood flow. They account for about 80% of the resistance to blood flow in your body, which makes them critical for maintaining steady blood pressure.
Each smooth muscle cell in an arteriole wall has its own dedicated nerve connection, giving your nervous system precise control over how wide or narrow each vessel gets. When an arteriole constricts to half its diameter, blood flow through it drops to just one-sixteenth of what it was. This is how your body redirects blood where it’s needed most, sending more to your muscles during exercise, for example, or to your digestive system after a meal.
Once blood passes through the arterioles and enters the capillaries, the walls are just one cell thick. That’s where the real work of the circulatory system happens: oxygen and nutrients pass out to surrounding tissues, and waste products like carbon dioxide pass in. From the capillaries, blood collects into tiny venules and then veins, which carry it back to the heart to start the cycle over again.
Arteries vs. Veins at a Glance
- Direction: Arteries carry blood away from the heart. Veins carry blood toward the heart.
- Pressure: Arteries operate under high pressure. Veins operate under low pressure.
- Wall thickness: Arteries have thick, muscular walls. Veins have thinner, more flexible walls.
- Oxygen content: Most arteries carry oxygen-rich blood, except pulmonary arteries. Most veins carry oxygen-poor blood, except pulmonary veins.
- Valves: Arteries rely on thick walls and elastic recoil to keep blood moving forward. Veins use one-way valves to prevent blood from flowing backward.