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The heart is an automatic pump that supplies blood to the entire body. Red blood cells in the blood contain oxygen, so the blood is the main transporter of oxygen to every organ, tissue, and even every cell in your body. So, how does this system work?

The heart is made up of four main chambers. There are two large chambers on the bottom (ventricles) and two smaller chambers stacked directly on top (atria). All the blood going through your veins (the blue lines you see beneath your skin)flows towards the heart. This blood has bluish color, because all the oxygen has been released into the body's tissues. The non-oxygenated blood collects into two main veins called the Superior Vena Cava and Inferior Vena Cava. These two large "hoses" of blood, empty into the top chamber of the heart, on the right side; the right atrium. Between beats, as your right ventricle relaxes, the blood is pumped from the right atrium (on top), to below, into the right ventricle. Your heart beats and the blood from this ventricle is pumped into the lungs. In the lungs, oxygen is transported into the blood through small blood vessels (capillaries). This now oxygenated blood (red) flows into the top left chamber of the heart, the left atrium. Again, as the ventricle relaxes after a beat, the blood is pumped into the left ventricle. Another beat of the heart and all this blood, with lots of oxygen in it, it pumped to the entire body. The tissues of the body take the oxygen they need and all the blood eventually returns back to the veins. The cycle starts all over again.

All this is controled by your body, without ever having to think about it. This magnificant event takes place over 100,000 times a day. No wonder we are so tired when we finally get into bed at night!

Learn more about this author, John Webb.
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