Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Cardiovascular System
Vessels of the Pulmonary Circulation

The pulmonary trunk (truncus pulmonalis), which is the largest vessel of the lesser (pulmonary) Circulation, originates from the right ventricle of The Heart. Beneath the aortic arch, it divides into the right and left pulmonary Arteries. The ligamentum arteriosum extends from the bifurcation of the pulmonary trunk to the aortic arch; it represents the obliterated ductus arteriosus (Botallo's duct) that closes after birth. The pulmonary arteries form part of the ROOT of the lung. Although classified as arteries, these vessels carry deoxygenated (venous) Blood rather than oxygenated blood. They terminate in the Hemomicrocirculatory bed (HMCB) of the Lungs, where the capillaries entwine the alveoli and contribute to The formation of the blood-air barrier. Here, Carbon dioxide is eliminated and Hemoglobin is saturated with oxygen, thereby producing oxygenated blood.

Converging together, the pulmonary capillaries transition into postcapillary venules and subsequently into venules that coalesce to form intra-organ Veins. Two Pulmonary veins emerge from the hilum of each lung, eventually draining into the left atrium and transporting oxygenated blood back to the heart.