describe blood circulation in short
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Answer :
During the time when the muscles of all four chambers of the heart are relaxed, the blood returning to the heart under low pressure in the veins enters the two atria. Blood from large veins, called vena cava, pours into right atrium. This blood comes from head, upper body parts and upper body parts where oxygen has been used up and the blood is free from oxygen (deoxygenated). Thus, the deoxygenated blood enters the right atrium. At the same time, the pulmonary vein from lungs pours oxygenated blood into the left atrium. Thus, the oxygenated blood enters the left atrium.
As the right and left atria fill with blood, pressure in them rises so that the valves between the left atrium and left ventricle and between right atrium and right ventricle open and the atria contract. Atrial contraction forces pumping of deoxygenated blood from right atrium into the right ventricle through tricuspid valve and oxygenated blood from left atrium into left ventricle through bicuspid valve.
Almost immediately the ventricles contract. This is called ventricular systole. During contraction of ventricles, the deoxygenated blood from right ventricle flows to the lungs through pulmonary artery and the oxygenated blood from left ventricle is distributed to the all parts of the body through the largest artery, called aorta.