Heart & circulation

Blood is flowing in your body all the time, day and night, without a break. It brings oxygen and nutrients to every cell and picks up waste again. So that the blood does not stand still, it needs a pump. This pump is your heart, and together with the blood vessels it forms the circulation.

The heart as a pump

The heart is a muscle, about as big as your fist. It contracts again and again and squeezes the blood out. After that it relaxes and fills up again. This squeezing and relaxing repeats your whole life long, all by itself, without you having to think about it.

Arteries and veins

The blood flows in tubes called blood vessels. Arteries carry the blood away from the heart into the body. Veins bring the blood back again to the heart. In between lie the capillaries, tiny vessels with a wafer-thin wall. That is exactly where the blood hands its oxygen to the cells. This forms a closed circle.

Where does the oxygen come from that the blood hands out? From the lungs. That is why the blood also runs a second, shorter loop: from the heart to the lungs, where it picks up oxygen, and then back to the heart. Only after that does it go out into the body again.

The pulse

With every beat the heart pushes a surge of blood into the arteries. You can feel this small pressure wave wherever an artery lies close under the skin, for example at the wrist or at the side of the neck. That is your pulse. If you count how often it taps in one minute, you know how often your heart beats.

Rest and effort

At rest a school child's heart beats about 80 times a minute, in adults it is more like 60 to 80 beats. When you run or jump, your muscles need more oxygen. Then the heart beats faster and pumps more blood, during wild play it can reach 160 beats a minute and more. If you take a break, the pulse slows down again. This way the circulation always adjusts to what you are doing.