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Lesson 04 – Your Cardiovascular System

Read About Your Cardiovascular System


Read the vocabulary terms to understand the reading better.


Arteries are the larger tubes that carry blood from the heart to all parts of the body.


Capillaries are extremely tiny blood vessels that connect the ends of the smallest arteries with the beginnings of the smallest veins.

Cardiovascular System

The cardiovascular system is the system of parts that include the heart, arteries, and veins that move blood throughout the body.


Plasma is the clear, yellowish liquid part of blood.


Platelets are very tiny disk-shaped particles in the blood of mammals that play an important role in blood clotting.

Red Blood Cells

Red blood cells are a disk-shaped cell that carries oxygen to the tissues and carries carbon dioxide from the tissues.


A system is a group of closely related parts that work together and rely on each other to function as a whole and complete unit.


Veins are a branching system of tubes that carry blood in the body.

White Blood Cells

White blood cells are cells in the blood that protect the body from invading infections and bacteria and fight against them.

Your Cardiovascular System

A system is made up of parts that all work together to make something happen. Your cardiovascular system is made up of your heart, blood, and blood vessels.

The cardiovascular system moves blood from your heart to every part of your body, then back to your heart again.


Your heart is a muscle about the size of your fist. When your heart beats, first it squeezes blood out of the heart and into blood vessels. Then it relaxes, which pulls more blood into the heart. When you are not being active, your heart beats about 70 times each minute. It beats faster when you are being active.


Most of your blood is a clear liquid called plasma. Red blood cells make blood look red. These blood cells carry oxygen to all the parts of your body. White blood cells help your body fight germs. Platelets are blood cells that work at repairing your body after an injury.

Blood Vessels

Blood vessels are tubes that your blood moves through. There are different types of blood vessels:

Arteries: These are blood vessels that carry blood away from the heart.

Veins: Veins are blood vessels that carry blood back to the heart.

Capillaries: Arteries and veins branch out into many smaller blood vessels, just like a large tree branch has many smaller branches on it. These smaller blood vessels are called capillaries.

Did You Know?

A human hair is 10 times thicker than most capillaries!

Blood and Oxygen

One of the most important jobs of blood is to carry oxygen to all parts of your body. How does oxygen get into the blood?

You breathe air down into your lungs. The air contains oxygen. Your heart pumps blood to your lungs. Oxygen in your lungs goes into your blood. This blood, which now has a fresh supply of oxygen, travels back to your heart. Then the blood is pumped through your body so it can deliver oxygen to all parts of your body.

Fun Facts!

  • If you took all the arteries, veins, and capillaries from an adult and laid them end to end, they would be long enough to go around the world two and a half times.
  • In one tiny drop of blood, there are about 5 million red blood cells.
  • A red blood cell dies after about four months. New red blood cells are made inside your bones.
  • There is a lot of blood in your legs because gravity pulls the blood down. Since there is no gravity in outer space, astronauts on a space mission have less blood in their legs, and more blood in their chest and head.

To learn more about your cardiovascular system, watch the video by Coach Meger Fitness Games on Youtube.


Now Show What You Know!

Complete some questions about the reading selection by clicking “Begin Questions” below.