<P> A separate system known as the bronchial circulation supplies oxygenated blood to the tissue of the larger airways of the lung . </P> <P> Deoxygenated blood leaves the heart, goes to the lungs, and then re-enters the heart; Deoxygenated blood leaves through the right ventricle through the pulmonary artery . From the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle . Blood is then pumped from the right ventricle through the pulmonary valve and into the main pulmonary artery . </P> <P> From the right ventricle, blood is pumped through the semilunar pulmonary valve into the left and right main pulmonary arteries (one for each lung), which branch into smaller pulmonary arteries that spread throughout the lungs . </P> <P> The pulmonary arteries carry deoxygenated blood to the lungs, where carbon dioxide is released and oxygen is picked up during respiration . Arteries are further divided into very fine capillaries which are extremely thin - walled . The pulmonary vein returns oxygenated blood to the left atrium of the heart . </P>

Where does blood flow from when it passes through the semilunar valve and into the lungs