The heart is situated in the middle of your chest, behind the breast bone. The heart is made of cardiac muscle. This muscle does not get tired like the muscles of your legs and arms do. The circulatory system is referred to as a double system because there are two separate circuits through which blood flows.

*in one circuit, blood flows from the heart to the body and back to the heart. This circuit carries nutrients and oxygen to the cells and carbon dioxide and waste away from the cell.

*in the second circuit, blood flows from the heart to the lungs and back again. The blood that arrives at the lungs is known as deoxygenated blood. This is blood that has very little oxygen in it

	Criado por Fatima Syeda mais de 5 anos atrás

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