The heart never stops pumping blood round the body. It is made of strong muscle and surrounded by the muscle are four chambers. The heart muscle beats by itself. The heartbeat varies because of messages from the brain as well as chemicals called hormones in the blood.
Bright red blood with oxygen comes to the heart from the lungs. It passes through a valve from the left atrium into the left ventricle, which pumps it round the body. Some of the oxygen is used as the blood travels round the body; it then looks darker. When it gets back to the heart a valve opens in the right atrium, which lets the blood into the right ventricle, which in turn pumps it to the lungs.
The cycle of the heart pump: - Blood from the body enters the right atrium; oxygen-rich blood from lungs enters the left atrium. The atria contract, pushing the blood into the ventricles. Valves close to stop blood flowing backwards; the ventricles contract, the ‘new’ blood goes to the aorta to travel round the body, and the ‘old’ blood goes to the lungs to pick up oxygen.
· The pulse you can feel is the expansion of the arteries each time the heart beats. Put a finger on the artery just above your wrist. How many times can you feel it in a minute? This is the rate at which your heart beats.
· An average heart beats about 70 times every minutes, or over 100000 times a day. Each minute it pumps about 5 litres of blood around the body.
· At birth a baby’s heart weighs about 22 g. An adult’s heart weighs nearly 20 times as much , about 450 g.
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