The Circulatory System [Blood Vessels]

• coronary artery

• pulse

• diffusion

• blood pressure

Vocabulary

• What are the structures and functions of arteries?

• What are the structures and functions of capillaries and veins?

• What causes blood pressure

Key Concepts

A Closer Look At Blood Vessels

Like corridors in a large building, blood vessels run through all of the tissues of your body. Although some blood vessels are as wide as your thumb, most of them are much finer than a human hair. If all the arteries, capillaries, and veins in your body were hooked together end to end, they would stretch a distance of almost 100,000 kilometers. That's long enough to wrap around Earth twice - with a lot left over!

Discover Activity

How Does Pressure Affect Blood Flow?

1. Spread paper bags over a table. Then, fill a plastic squeeze bottle with water.

2. Hold the bottle over a baking pan. Squeeze the bottle with one hand. Observe how far the water travels. CAUTION: Wipe up spills on the floor to prevent anyone from slipping.

3. Now, grasp the bottle with both hands and squeeze again. Observe how far the water travels this time.

Arteries

When blood leaves the heart, it travels through arteries. The right ventricle pumps blood into the arteries that go to the lungs. The left ventricle pumps blood into the aorta. Smaller arteries, called the coronary arteries, carry blood to the heart itself. Other branches carry blood to the brain, intestines, and other organs. Each artery branches into smaller and smaller arteries.

coronary arteries - small arteries that carry blood to the heart itself

Multiple Choice

True or False

When blood leaves the heart, it travels through arteries.

• True

• False

Multiple Choice

What are smaller arteries that carry blood to the heart itself?

• Aorta

• Veins

• Capillaries

• Coronary Arteries

Artery Structure

The walls of arteries are generally very thick. In fact, artery walls consist of three cell layers. The innermost layer, which is made up of epithelial cells, is smooth. The smooth surface enables blood to flow freely. The middle layer consists of mostly muscle tissue. The outer wall is made of flexible connective tissue. Because of this layered structure, arteries have both strength and flexibility. Arteries are able to withstand the enormous pressure of blood as it is pumped by the heart and to expand and relax between heart beats.

​

Connective Tissue -

Smooth Muscle -

- Layer of epithelial cells

Multiple Choice

How many cell layers make up the artery walls?

• One

• Two

• Three

• Four

Pulse

If you lightly touch the inside of your wrist, you can feel the artery in your wrist rise and fall repeatedly. This pulse is caused by the alternating expansion and relaxation of the artery wall. Every time the heart's ventricles contract, they send a spurt of blood out through all the arteries in your body. As this spurt travels through the arteries, it pushes the artery walls and makes them expand. After the spurt passes, the artery walls relax and become narrower again.

When you count the number of times an artery pulses beneath your fingers, you are counting heartbeats. By taking your pulse rate, you can determine how fast your heart is beating.

pulse - the alternating expansion and relaxation of the artery wall

Multiple Choice

What is caused by the alternating expansion and relaxation of the artery wall?

• Pulse

• Headache

• Bile

Multiple Choice

True or False

When you count the number of times an artery pulses beneath your fingers, you are counting pulse beats.

• True

• False

Regulating Blood Flow

The layer of muscle in an artery acts as a control gate, adjusting the amount of blood sent to different organs. When the muscle contracts, the opening in the artery becomes smaller. When the muscle relaxes, the opening becomes larger. For example, after you eat, your stomach and intestines need a greater blood supply for digestion. The arteries leading to those organs open wider, and more blood flows through them. In contrast, when you are running, your stomach and intestines need less blood than the muscles in your legs. The arteries leading to the digestive organs become narrower, decreasing the blood flow to these organs.

Lesson Complete

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