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Working of the heart

                           WORKING OF HEART  

Blood from different parts of the body comes to right atrium, when it expands. Blood is brought from upper part of the body through superior vena cava and from lower part of the body through inferior vena cava.  When right atrium contracts, the blood goes to right ventricle. The atrioventricular aperture is closed by a valve after blood transfer. Valves prevent backflow of blood when the atria or ventricle contracts. 

  When the right ventricle contracts, blood forced out to the lungs for oxygenation through pulmonary artery, guarded by another valve. In lungs the exchange of gases takes place, blood give off carbon dioxide and takes in oxygen from lungs. Pulmonary vein brings oxygenated blood from lungs to the left atrium, as it relaxes. When the left atrium contract, the blood is transferred to left ventricle, which expands. The aperture between left atrium and ventricle is guarded by another valve. The wall of ventricle is three or four times thicker than those of right ventricle, as it pumps blood to all the parts of the body. When left ventricle contracts the oxygen-rich blood is pumped into aorta for circulation to different parts of the body. The opening of aorta is also guarded by a valve. Deoxygenated blood is collected by small veins, opens into larger veins, which brings blood back to the right atrium. 


  One sequence of the filling of the heart with blood and its pumping is called the cardiac cycle. The phase of ventricle contraction is called systole and its relaxation phase is called diastole.   

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