The Heart
The heart actually is roughly the size of your fist. With the help of electrical signals sent by the nervous system it helps pump blood through out your body and keeps alive while doing it! The heart is made of cardiac muscle. Cardiac cells have an extremely high amount of mitochondria in their cells, that all help produce energy for the heart 24/7.
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The heart is composed of four chambers. The Atria on top, and ventricles on the bottom. When the heart beats the atria contracts (pull inwards, gets smaller) first, this squeezes the blood into the ventricles, the ventricles then contract , which forces the blood out of the heart and on into the body.
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