Pulmonary Circulation

The pulmonary circulation, also known as the lesser circulation, is a part of the cardiovascular system whose function is to bring venous blood (oxygen-poor, carbon dioxide-rich blood) into contact with the pulmonary alveoli via the pulmonary arteries, to fully reoxygenate it, and then return this blood to the heart via the pulmonary veins. The bronchial circulation feeds the bronchial tubes and pleura with oxygenated blood via the bronchial arteries, and returns deoxygenated blood to the heart via the bronchial veins (en), which drain into the azygos vein.The small circulation is a high-flow (100% of cardiac output) but low-pressure system, with maximum pressure not normally exceeding 25 millimeters of mercury in the pulmonary artery. The circulation is pulsatile. It comprises two parts: arterial and venous microcirculation, and capillary microcirculation. From the atrium, venous blood passes into the right ventricle, from where it is propelled into the pulmonary arteries, then crosses the pulmonary capillaries where gas exchange takes place, and finally returns to the left atrium via the pulmonary veins.