<P> A separate system known as the bronchial circulation supplies oxygenated blood to the tissue of the larger airways of the lung . </P> <P> The earliest human discussions of pulmonary circulation date back to Egyptian times . Human knowledge of pulmonary circulation grew gradually over centuries, and scientists Ibn al - Nafis, Michael Servetus, and William Harvey provided some of the first accurate descriptions of this process . </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> 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>

Through which vessel does blood leave the heart to go to the lungs