The circulatory system distributes blood to and from cells throughout the body. The heart pumps blood which carries oxygen, nutrients, hormones and waste products. The heart has four chambers - the two upper atria receive blood while the two lower ventricles pump blood out. Blood contains red blood cells which carry oxygen and white blood cells which fight infection. Blood vessels include arteries carrying oxygenated blood away from the heart and veins carrying deoxygenated blood back to the heart via the lungs.
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