As the heart beats, it pumps blood through a system of blood vessels called the circulatory system. The blood that these vessels carry is essential for the body to function. Blood carries oxygen and nutrients to your body's tissues, assists in the removal of carbon dioxide and waste products, and promotes the overall health of the body's tissues. There are three main types of vessels that make up this system:
Arteries carry oxygen-rich blood away from the heart to the body's tissues. Veins take oxygen-poor blood back to the heart. Capillaries are small thin blood vessels that connect the arteries and the veins.
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying into the right atrium. Blood flows from the right atrium into the right ventricle through the tricuspid valve. Blood then leaves the right ventricle and the heart through the pulmonic valve into the pulmonary artery and to the lungs. Oxygenated blood returns from the lungs to the heart via the pulmonary vein into the left atrium. From the left atrium, blood flows to the left ventricle through the mitral valve. From the left ventricle blood leaves the heart through the aortic valve into the aorta and to the body.
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