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Hi, I'm Jim Shields for About.com, and today I'm going to teach you about the circulatory system.  The circulatory system is essentially a transportation system to move things through the body. Made up of two systems, the cardiovascular system and the lymph system, the circulatory system delivers nutrients to and removes waste from the cells. The cardiovascular system is responsible for moving blood to and from the heart. It has three parts: the heart, the blood and the blood vessels. The heart uses two pumps to circulate blood through our blood vessels: one to send oxygenated blood to the body and the other to send deoxygenated blood back to the lungs to receive oxygen.The cardiovascular is a closed system, which means that the blood never leaves the blood vessels and heart. Nutrients, dissolved gases like oxygen, and waste products can move into and out of the bloodstream, but the blood is meant to stay in the system. The lymphatic system is another part of the circulatory system, which is significantly different from the cardiovascular system in both purpose and design. Instead of delivering nutrients and oxygen, which are the primary purposes of the cardiovascular system, the lymphatic system moves white blood cells, or lymphocytes, which fight infection. It also carries waste products like undigested proteins and other debris away from the cells. Another difference is that the lymphatic is unidirectional, traveling always toward the heart, and emptying into the subclavian veins on either side of the neck.   But if it moves only in one direction, what is the source of lymph? Where does it come from? This question leads to another difference between lymphatic and cardiovascular. The lymphatic system is an open system. When plasma is delivered to the cells from the smallest arteries, and it has dropped off nutrients, oxygen and hormones, most of it reenters the blood vessels and is delivered back to the heart.But about three of the twenty pints of blood in the typical cardiovascular system does not make it back into the bloodstream, but becomes interstitial fluid outside the cardiovascular system. The lymphatic system delivers this excess fluid back to the heart to regulate the supply of blood. Because there is no pump in the lymphatic like there is in the heart, it requires the voluntary movement of muscles in order for it to get around.  So remember, the circulatory system consists of the cardiovascular system, which is the heart, blood and blood vessels, and the lymphatic system, which is a network of tiny vessels that carry lymph toward the heart. Thanks for watching. To learn more about biology, visit us on the web at About.com.
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