Pulmonary artery

A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the main pulmonary artery or pulmonary trunk from the heart, and the smallest ones are the arterioles, which lead to the capillaries that surround the pulmonary alveoli.

The pulmonary arteries are blood vessels that carry systemic venous blood from the right ventricle of the heart to the microcirculation of the lungs. Unlike in other organs where arteries supply oxygenated blood, the blood carried by the pulmonary arteries is deoxygenated, as it is venous blood returning to the heart. The main pulmonary arteries emerge from the right side of the heart and then split into smaller arteries that progressively divide and become arterioles, eventually narrowing into the capillary microcirculation of the lungs where gas exchange occurs.^{[citation needed]}

In order of blood flow, the pulmonary arteries start as the pulmonary trunk that leaves the fibrous pericardium (parietal pericardium) of the ventricular outflow tract of right ventricle (also known as infundibulum or conus arteriosus. The outflow track runs superiorly and to the left, posterior to the pulmonary valve. The pulmonary trunk bifurcates into right and left pulmonary arteries below the arch of aorta and in front of the left main bronchus. Pulmonary trunk is short and wide – approximately 5 centimetres (2.0 in) in length and 2 centimetres (0.79 in)-3 centimetres (1.2 in) in diameter.

The pulmonary trunk splits into the right and the left main pulmonary artery. The left main pulmonary artery is shorter than the right, passes behind and downwards the descending aorta and above the left main bronchus to the root of the left lung. Above, the left main pulmonary artery is connected to the concavity of the proximal descending aorta by the ligamentum arteriosum. The right pulmonary artery pass across the midline of the body, below the carina of trachea, and comes in front of the right main bronchus.

The left main pulmonary artery then divides into two lobar arteries, one for each lobe of the left lung.

At the right root of the lung, it bifurcates into artery that supplies the right upper lobe of the lung, in front of the right upper lobe bronchus, and interlobar artery that supplies the right middle and inferior lobes of the lung, running together with bronchus intermedius.

The right and left main pulmonary (lungs) arteries give off branches that supplies the corresponding lung lobes. In such cases it is termed lobar arteries. The lobar arteries branch into segmental arteries (roughly 1 for each segment). Segmental arteries run together with segmental bronchi, at the posterolateral surfaces of the bronchi. These in turn branch into subsegmental pulmonary arteries. These eventually form intralobular arteries. The pulmonary arteries supply the alveoli of the lungs. In contrast, bronchial arteries, that has different origins, supply the bronchi of the lungs.

The pulmonary arteries originate from the truncus arteriosus and the sixth pharyngeal arch. The truncus arteriosus is a structure that forms during the development of the heart as a successor to the conus arteriosus.