Arteries and veins (also called blood vessels) are tubes of muscle that your blood flows through. Arteries carry blood away from the heart to the rest of the body. Veins push blood back to your heart. You have a complex system of connecting veins and arteries throughout your body.
Basics of Blood Flow
Veins and arteries play important roles in your breathing ( respiratory) and blood flow (circulatory) systems. Understanding these systems can help you understand how your veins and arteries work.
When you breathe, you inhale oxygen from the air. Your body needs oxygen for chemical reactions that produce energy and keep you alive. Carbon dioxide is a waste product of these chemical reactions. Your body needs to get rid of the carbon dioxide, or serious health problems can happen.
When you inhale, your lungs absorb the oxygen and transfer it into your blood. The high-oxygen blood enters your heart, which pumps it into your arteries throughout your body. The blood gives oxygen to cells that need it for chemical reactions, and absorbs waste carbon dioxide along the way.
The high-carbon dioxide blood eventually flows back through your veins to your heart. Your heart pumps it back into your lungs where it started. Breathing out releases the extra carbon dioxide from your blood. You inhale to replenish oxygen, and the cycle starts again.
What Are Arteries?
Your arteries carry high-oxygen blood away from your heart towards the rest of the body. They branch out into many smaller arteries in other parts of your body.
Your largest artery is the aorta. This is the first artery your blood travels through after getting new oxygen from your lungs. The aorta starts at your heart and reaches up toward your neck. Smaller arteries branch off of the aorta and go up to your head.
The aorta then curves back down to your chest. It continues through your abdomen and ends at your groin. Along the way, it splits off into other arteries that deliver oxygen-rich blood to your arms, legs, and the rest of your body.
What Are Veins?
Your blood loses oxygen as it travels through your arteries. Veins carry the blood back to your heart to absorb more oxygen. Your veins usually hold about 75% of all the blood flowing through your body.
Your largest veins are the superior and inferior vena cava. Your superior vena cava carries blood from your upper body to the heart. Your inferior vena cava carries blood from everywhere below your heart. Like arteries, these two veins branch off into many other veins throughout your body.
Unlike arteries, veins generally need to work against gravity to push blood back to your heart. Veins have valves to help with this. These are one-way pairs of flaps inside a vein. They open for blood that’s heading upwards toward the heart, and close to keep blood from flowing back downwards.
Muscle surrounds most veins in your body. When you walk, run, or otherwise use your muscles, they make a squeezing motion. These squeezes push against the vein and force the blood upwards toward your heart.
How Arteries and Veins Work Together
Arteries and veins work together to keep blood flowing throughout your body smoothly. They connect through structures called capillaries. Capillaries are small webs of thin tubes that connect to an artery on one side and a vein on the other.
You have capillaries throughout your body. Some parts of your body have more capillaries depending on how much energy they need. For example, your muscles use a lot more energy than your skin, which is why your muscles have more capillaries than your outer skin.
What Are Arteries and Veins Made Of?
Arteries and veins both have three main layers. The innermost layer, which blood touches directly, is made of stretchy tissue. The middle layer is made of muscle tissue that helps blood vessels hold their shape. The outer layer is also stretchy, which helps vessels expand or shrink easily with varying amounts of blood flow.
Blood moves more quickly through your arteries. Your arteries are thicker and stretchier to be able to handle the higher pressure of blood moving through them. Your veins are thinner and less stretchy. This structure helps veins move higher amounts of blood over a longer time than arteries.
Health Risks Involving Veins and Arteries
Problems with your veins and arteries can lead to many different health issues. Some of the most common include:
Varicose veins. Sometimes your veins have trouble getting blood back up to your heart. This can result in varicose veins, which can look like the veins are bulging out of your skin. It happens most often on your legs.
Varicose veins usually aren't serious. They can cause soreness and pain, and often occur in people who are overweight.
Artery plaque. Over time, cholesterol and other materials, collectively called plaque, can build up inside your arteries. This is called atherosclerosis.
Plaque buildup in your arteries weakens blood flow throughout your body. It can lead to heart disease, gangrene, and stroke.