THE CIRCULATORY SYSTEM
Blood continuously circulates around the body to supply the body’s tissues with food and oxygen and to clear them of waste products.Blood leaves the heart through larges vessels called arteries,then passes to smaller vessels called arterioles.Arterioles lead to every organ and tissue in the body,including the heart.From there,blood moves to tiny vessels called capillaries,where there is an exchange of oxygen and nutrients for waste products.On the way back to the heart,the process is reversed;blood moves to small veins,which merge into the superior and inferior vena cava;they receive blood from the upper and lower body,respectively.The veins take blood to the right side of the heart;then it is taken to the lungs via the pulmonary artery,where oxygen is absorbed and carbon dioxide breathed out.The oxygen-rich blood then flows into the pulmonary vein,into the left side of the heart,and the circuit begins again.
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