What are Arteries? - Function & Definition

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  • 0:02 What Is an Artery?
  • 0:16 Arterial Divisions
  • 2:26 Arterial Structure
  • 4:30 Atherosclerosis
  • 5:18 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
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.

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.

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