How the heart works

The left auricle receives oxygenated blood from the lungs through the Pulmonary vein. The left auricle has a thin wall and therefore contracts feebly to send oxygenated blood under low pressure into the left ventricle through the opened bicuspid valve. The left ventricle has a very thick wall. It therefore contracts powerfully to send oxygenated blood under a very high pressure out of the ventricle to be supplied to all parts of the body. 
As the left ventricle contracts, the bicuspid closes, while the aortic semilunar valve at the exit aorta opens. Oxygenated blood flows through the aorta to be supplied to all parts of the body. There is a small branch of the aorta which supplies oxygenated blood to the heart muscle. This branch is called the coronary artery. Another branch of the aorta supplies oxygenated blood to the head and arms. The main part of the aorta called dorsal aorta supplies oxygenated blood to the body below the heart. The superior vena cava from the head region of the body and the inferior vena cava from the lower part of the body bring deoxygenated blood to the right auricle. When the right auricle contracts, the deoxygenated blood flows into the right ventricle via the tricuspid valve. When the right ventricle contracts, the tricuspid valve closes and the blood flows out of the right ventricles via the semi-lunar valve into the pulmonary artery. The pulmonary artery is the only artery that carries deoxygenated blood. It carries deoxygenated blood to the lungs.


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