Human Anatomy and Physiology - N. I. Fedyukovich 2003

Cardiovascular System
Blood Vessels of the Pulmonary Circulation

The Pulmonary Circulation begins in the right ventricle, from which the pulmonary trunk emerges, and ends in the left atrium, into which the Pulmonary Veins empty. Also known as the lesser or pulmonary circuit, it facilitates gas exchange between the Blood in the pulmonary capillaries and the air within the pulmonary alveoli. It comprises the pulmonary trunk, the right and left pulmonary Arteries with their respective branches, and the pulmonary vessels that converge into two right and two left pulmonary veins, which empty into the left atrium.

The pulmonary trunk (truncus pulmonalis) originates from the right ventricle of The Heart, has a diameter of 30 mm, courses obliquely upward and to the left, and bifurcates at the level of the fourth thoracic vertebra into the right and left pulmonary arteries, which HEAD toward their respective Lungs.

The right pulmonary artery, with a diameter of 21 mm, runs to the right toward the hilum of the lung, where it divides into three lobar branches, each of which further branches into segmental branches.

The left pulmonary artery is shorter and narrower than the right, running transversely from the bifurcation of the pulmonary trunk to the hilum of the left lung. Along its path, the artery crosses the left main bronchus. At the hilum, corresponding to the two lobes of the lung, it divides into two branches. Each branch then subdivides into segmental branches: one supplies the upper lobe, while the other—the basal part—provides blood via its branches to the segments of the lower lobe of the left lung.

Pulmonary veins. Venules originate from the pulmonary capillaries and merge into larger veins, forming two pulmonary veins in each lung: the right superior and right inferior pulmonary veins, and the left superior and left inferior pulmonary veins.

The right superior pulmonary vein collects blood from the upper and middle lobes of the right lung, whereas the right inferior pulmonary vein drains the lower lobe of the right lung. The common basal vein and the superior vein of the lower lobe combine to form the right inferior pulmonary vein.

The left superior pulmonary vein collects blood from the upper lobe of the left lung. It features three branches: the apicoposterior, the anterior, and the lingular.

The left inferior pulmonary vein drains blood from the lower lobe of the left lung; it is larger than the superior pulmonary vein and consists of a superior vein and a common basal vein.