How does heart act as a pump?
Blood reaches the right atrium from the superior and inferior vena cavae. It passes to the right ventricle through the tricuspid valve, which opens in diastole. In systole, tricuspid valve closes and right ventricular contraction pushes the blood to the pulmonary artery across the pulmonary valve. Pulmonary valve closes in diastole and prevent back flow into the right ventricle when it relaxes. Similarly tricuspid valve closes in systole to preven back flow into the right atrium when the right ventricle contracts. Blood reaches the lungs from the pulmonary artery and gets oxygenated. It returns to the left atrium through the pulmonary veins. From the left atrium the blood reaches the left ventricle through the bicuspid (mitral valve). Mitral valve opens in diastole and closes in systole, when the left ventricle ejects blood into the aorta through the aortic valve. Aortic valve closes in diastole to prevent backflow of blood into the left ventricle when it relaxes.