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In this lesson, you will learn about arteries and how they function.

You’ll also become familiar with the names of some important arteries and find out how the vessels are structured. At the end of the lesson, you’ll also have the chance to test your new knowledge of arteries with a brief quiz.

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What Is an Artery?

An artery is a vessel that carries blood away from the heart and toward other tissues and organs. Arteries are part of the circulatory system, which delivers oxygen and nutrients to every cell in the body.

Arterial Divisions

Much like the cooling system in your car, which pushes fluid from the radiator, through the engine block and back to the radiator, your circulatory system is a ‘closed loop’ consisting of your heart, arteries, arterioles, capillaries, venules and veins. Blood leaves your heart through your arteries, travels into progressively smaller arterioles, enters thin-walled capillaries (where oxygen and nutrients are delivered to your tissues), flows into progressively larger venules and finally returns to your heart via your veins.There are two arterial divisions within your body: pulmonary and systemic.

‘Pulmo’ is the Latin root for ‘lung.’ The pulmonary division, which contains only the pulmonary arteries, is much shorter than the systemic division. The pulmonary arteries carry blood away from your heart and deliver it to your lungs, where the blood becomes oxygenated.

This oxygenated blood then returns to your heart through your pulmonary veins.The systemic division contains the aorta and all of its branches. From your heart, oxygenated blood is pushed into your aorta, which is the largest artery in your body.

Two smaller arteries – the coronary arteries – immediately branch off the aorta to supply oxygenated blood to the heart itself. As it arches over to travel downward to your abdomen, your aorta gives off branches that carry blood to your head and arms: the brachiocephalic artery, the left common carotid artery and the left subclavian artery.Entering the abdomen, your aorta sends additional branches to your stomach, liver, spleen, kidneys, intestine and other internal organs. Just below the level of your navel, your aorta divides into two arteries: the iliac arteries, which give off several more branches before coursing into your legs as your femoral arteries.From this brief description of arterial anatomy, you can see that the pulmonary arteries are the only arteries in your body that carry deoxygenated blood, while the entire systemic division carries oxygenated blood.

Arterial Structure

Your arteries are essentially living hollow tubes that conduct fluid, or blood, from one place to another. The walls of all arteries are composed of three layers: the tunica intima, tunica media and tunica adventitia, which are arranged one on top of the other like the layers of an onion. ‘Tunica’ simply means ‘coat.’

  • The tunica intima is the innermost layer of the arterial wall and the layer that is most intimate with your blood.
  • Next is the tunica media, or middle coat of the artery.
  • The outer layer of the artery is the tunica adventitia, which is also called the tunica externa.

The tunica intima, which is in full-time contact with your blood, is itself composed of three layers. A thin, inner layer of endothelial cells provides a smooth, almost frictionless surface that allows your blood to flow freely through the artery. Surrounding the endothelial cells is a thin layer of connective tissue, which is then coated by a fine network of elastic fibers that help support the tunica intima and attach it to the next layer, which is the tunica media.The tunica media, which is composed of elastic fibers and muscle, is the thickest layer of an artery’s wall.

The elasticity of the tunica media allows your arteries to expand with each heartbeat and to contract when the heart rests. The inward-and-outward movement of your arterial walls, which can be detected as a pulse in any of your major arteries, helps push your blood forward. The muscles in the tunica media help control your blood pressure by widening or narrowing the inner diameter of your arteries.The tunica adventitia, which is the outermost layer of the arterial wall, is primarily composed of elastic fibers and collagen, a protein that makes up all of the connective tissue in your body. The tunica adventitia is tough enough to support the artery and anchor it to surrounding structures, but elastic enough to allow the arterial wall to expand and contract in response to your heartbeat.

Hardening of the Arteries (Atherosclerosis)

Atherosclerosis, or hardening of the arteries, results from the buildup of cholesterol-containing plaques along the inner walls of your arteries. Atherosclerosis causes gradual narrowing of your arteries, which reduces blood flow and interferes with oxygen delivery to your tissues and organs. In addition to reducing oxygen delivery by impairing blood flow, atherosclerotic plaques can fracture or break open. This triggers clotting, which can cause sudden blockage of an artery.

Smoking, high cholesterol, obesity, a lack of physical activity and diabetes are some of the factors that increase your risk for developing atherosclerosis. Atherosclerosis is the primary cause of heart attacks and strokes in developed countries and is, in fact, the leading cause of death in the Western world.

Lesson Summary

Arteries are vessels that carry blood away from the heart. They are part of your circulatory system, which is a closed loop that delivers blood and nutrients to every cell in your body.

With the exception of the pulmonary arteries, which carry deoxygenated blood to your lungs, all of your arteries carry oxygenated blood. Your arterial system is in two divisions: pulmonary and systemic.Arteries are hollow tubes whose walls consist of three layers: tunica intima, tunica media and tunica adventitia.

The tunica intima itself is composed of three layers, including connective tissue, elastic fiber and endothelial cells. The arrangement of these layers allows your arteries to conduct blood smoothly to distant tissues and to expand and contract in response to your beating heart.Some of us may be at risk for atherosclerosis, in which the arteries harden and narrow. This occurs when cholesterol plaques build up, which can put you at risk for heart attacks and strokes.

Key Terms

Sketch of the Cross-section of an Artery
  • Artery – a vessel that carries blood away from the heart and toward other tissues and organs
    • Aorta – the largest artery in the human body; supplies oxygen to the circulatory system
    • Coronary arteries – two smaller arteries which branch off the aorta to supply oxygenated blood to the heart itself
    • Brachiocephalic artery – artery which carries oxygen to the head and arms
    • Carotid artery – an artery located in the front of the neck which carries oxygen-rich blood to the brain
    • Subclavian artery – an artery which supplies blood to the arm
    • Iliac arteries – the large arteries which branch out to supply blood to the lower trunk and the backs of the legs
    • Femoral arteries – arteries which carry oxygen to the legs
  • Circulatory system – the system of blood vessels which delivers oxygen and nutrients to every cell in the body
  • Oxygen – the life-supporting molecule in the air
  • Pulmonary division – a portion of arteries which contains only the pulmonary arteries; much shorter than the systemic division
    • Pulmonary arteries – arteries which carry blood away from a person’s heart and deliver it to his/her lungs, where the blood becomes oxygenated
  • Systemic division – a large portion of arteries which contains the aorta and all of its branches
  • Artery walls – the exterior portions of the hollow tubes which carry oxygen to different parts of the body; contain three layers
    • Tunica intima – the innermost layer of the arterial wall which comes in full contact with the blood
      • Endothelial cells – a thin, inner layer of cells in the tunica intima which provides a smooth, almost frictionless surface to allow blood to flow freely through the artery
      • Connective tissue – the thin layer of tissue surrounding the endothelial cells in the tunica intima
      • Elastic fibers – a fine network of fibers coating the connective tissue that help support the tunica intima and attach it to the tunica media
    • Tunica media – the middle layer of the arterial wall
    • Tunica adventitia – the outer layer of the arterial wall
    • Tunica externa – another name for tunica adventitia
  • Pulse – the inward-and-outward movement of arterial walls that helps push blood forward
  • Collagen – a protein that makes up all of the connective tissue in the body
  • Atherosclerosis – hardening of the arteries; results from the buildup of cholesterol-containing plaques along the inner walls of the arteries

Learning Outcomes

After this lesson, you should be feel ready to:

  • Define artery
  • Recall the purpose and parts of the circulatory system
  • Identify the anatomy and function of the pulmonary and systemic arterial divisions
  • Describe the structure of arteries
  • Explain what causes atherosclerosis and name some of the risk factors

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