1. The Circulatory System
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2. The Circulatory System
The circulatory system circulates (moves) your blood through your body.

3. Blood
Blood carries oxygen and digested nutrients to the cells and carbon dioxide and excess water from the cells.

4. Blood
Blood has a liquid part, called plasma, and a solid part, made up of blood cells.

5. Red Blood Cells
Red blood cells contain a substance called hemoglobin, which picks up the oxygen or carbon dioxide. They look like pinched disks.

6. White Blood Cells
White blood cells fight disease and infection by destroying foreign materials.

7. Platelets
Platelets are tiny, colorless pieces of cells that help stop bleeding by giving off a chemical that helps blood clot.

8. Blood Vessels
Blood vessels travelling away from the heart are called arteries. The blood in arteries is usually rich in oxygen and nutrients and appears red.

9. Blood Vessels
Blood vessels travelling back to the heart are called veins. The blood in veins is usually carrying carbon dioxide and waste materials and appears blue.

10. Blood Vessels
Arteries and veins are connected by very tiny capillaries that pass by the cells of the body.

11. The Heart
Blood flows through the heart, through each of the four chambers (sections of the heart). The right atrium takes the blood carrying carbon dioxide from all parts of the body and passes it through a valve (door) into the right ventricle.

12. The Heart
The right ventricle contracts (squeezes) and pumps the blood through the pulmonary artery to the lungs, where the blood gives up its carbon dioxide and picks up oxygen.

13. The Heart
The blood then returns along the pulmonary vein to the left atrium and passes through a valve into the left ventricle.

14. The Heart
The left ventricle then contracts and the now-oxygen-rich blood is pumped to the rest of the body.

15. Your Pulse
Note that both ventricles contract at the same time, squeezing the blood out of the heart. This movement creates a pulse.