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LET'S EXPLORE The human body

What does the heart do?

Diagram of blood circulationDiagram of blood circulationThe heart lies at the centre of what is called the circulatory system. This includes the lungs and the network of blood vessels that reaches to all parts of the body. The heart sucks in oxygen-filled blood from the lungs, then pumps it around the body through arteries. Meanwhile, veins bring used-up blood, containing carbon dioxide, back to the heart. The heart sends this blood to the lungs to get rid of the carbon dioxide and take in fresh oxygen. The cycle begins again.

How the heart worksHow the heart works

How the heart works

About the size of your fist, the heart is a powerful pump. As the muscles of the heart relax, blood enters its various “chambers”. Oxygen-filled blood from the lungs fills the red chambers in the diagram (left). At the same time, carbon-dioxide-filled blood from the rest of the body enters the blue chambers. 

The heart then squeezes and pumps the blood out. The oxygen-filled blood goes to the rest of the body, while the carbon-dioxide-filled blood goes to the lungs.

The first heartbeat in a human being happens in the fourth week of pregnancy.

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