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The Heart The Heart The Heart The heart is made up of four chambers. These are called the atria (left atrium, right atrium also known by the term auricles) and the left and right ventricles. The atria collect the blood. The ventricles pump the blood out of the heart. To prevent blood from flowing backwards, each chamber is equipped with a valve. The two sides of the heart are separated by the septum. The right side of the heart pumps de-oxygenated blood (blood not containing oxygen) to the lungs to pick up oxygen. The left side of the heart pumps the oxygenated blood from the lungs around the rest of the body. Take a minute to consider the difference between the circulatory system and the lymphatic system. Circulation has the heart to pump it while the lymph depends on muscular tone to compress it. Blood Vessels Blood is carried throughout the body through blood vessels. In an average day, the heart will pump around 36,000 quarts of blood through 12,450 miles of blood vessels. An adult has around 5-6 quarts of blood within. There are three types of vessels: Arteries These are the largest of the three and have very thick muscular walls. These create a very high pressure environment for the blood and carry blood away from the heart (this is always oxygenated with the exception of the pulmonary artery which goes to the lungs). The small passageways that allow the blood to flow through are called the internal lumen. Veins Smaller, veins have thinner walls and a larger internal lumen. The blood in the veins is contained under much lower pressure which also have valves to prevent back flow. Veins carry blood to the heart. In the case of veins, the blood is always de-oxygenated apart from the pulmonary vein which goes away from the lungs to the heart. Capillaries Capillaries are teeny weeny, measuring only one cell in thickness and constrict the blood under very low pressure. These are found in both the muscles and the lungs. Gas exchange takes place in the capillaries. Oxygen passes through the capillary wall and then pervades into the tissues. Carbon dioxide then passes from the tissues and is taken into the blood.