The pulmonary circulation is provided by two pulmonary arteries and four pulmonary veins.

Pulmonary arteries

The left and right pulmonary arteries arise below the aortic arch from the pulmonary trunk that emerges from the infundibulum (conus arteriosus) of the right ventricle of the heart. The pulmonary arteries divide into smaller branches that continue to branch further. Finally, the smallest arteries of the pulmonary circulation system are the pulmonary capillaries that form a network around the alveoli.

The right pulmonary artery passes horizontally to the right side posterior to the ascending aorta and superior vena cava. Near the pulmonary hilum, it divides into superior, middle and inferior branches, supplying the upper, middle and lower lobes of the right lung.
The left pulmonary artery passes posterosuperiorly, enters the hilum of the left lung, and divides into superior and inferior branches, which supply the upper and lower lobes of the left lung. The left pulmonary artery also gives a branch that supplies the lingula.

Pulmonary veins

Each lung contains two pulmonary veins, and they carry oxygenated blood from the lungs to the left atrium of the heart. They collect blood from the areas supplied by the pulmonary arteries.

The pulmonary veins arise from the pulmonary capillary network that joins together and forms larger vessels (pulmonary capillaries -> intrasegmental veins -> segmental veins -> intersegmental veins -> lobar veins -> pulmonary veins). The pulmonary veins emerge from each lung at the pulmonary hilum and flow into the left atrium of the heart. On their course, they also receive bronchial veins.

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Pulmonary circulation