1 As the two atria expand, contaminated blood from all over the body enters the right atrium through the upper and greater veins. At the same time pure blood from the lungs comes to the left atrium through the pulmonary veins.
2 When the atrium is filled with blood, it contracts and the atrium expands. Then the blood of the right atrium enters the right ventricle through the tripod valve and the blood of the left atrium enters the left atrium through the double ventricle valve.
3 6 The two ventricles constrict when they are full of blood and enter the lungs from the right ventricle through the pulmonary artery. From the left ventricle it spreads throughout the body through the arteries. During this time the crescent-shaped valve opens and the double-leaf and triple-leaf valves close.
4 6 After that, when the two atria expand, blood enters the atrium. Thus the system of blood circulation continues through contraction and expansion.👍👍
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