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Heart Work
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The heart and the blood vessels make up the cardiovascular or circulatory system of the body. The blood vessels are basically hollow tubes that carry blood, oxygen, nutrients, waste products and other substances around the body, pumped by the heart. The blood vessels are flexible and respond to changes in circumstances and circulating hormones by becoming wider (dilating) or narrower (constricting). Veins are the blood vessels that carry oxygen-poor blood to the heart and arteries carry oxygen-rich blood away from the heart. Arteries and veins are connected by tiny capillaries.
The average adult human heart is about the size of a clenched fist and weighs about 300 g. It lies in the middle of the chest (slightly to the left) behind the breastbone and between the lungs.
