All cells in the body receive food and oxygen through the circulatory system. In addition to being a delivery service, it's also a waste collection service for carrying waste products like carbon dioxide and urea to where they can be removed from the body. A circulatory system is made up of the heart, blood vessels, and blood itself.
The double circulatory system
The human body consists of two circulatory systems that are joined together:
To take in oxygen, the right ventricle pumps deoxygenated blood to the lungs in the first circuit. The blood is then pumped back to the heart.
The left ventricle pumps oxygenated blood around all the rest of the body's organs in the second circuit. Oxygen is given up by the blood in the cells and the deoxygenated blood is pumped out again into the lungs.
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