PA
Pulmonary Arteries
The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs for gas exchange. The pulmonary trunk arises from the right ventricle and divides into right and left pulmonary arteries, which enter the corresponding lungs and branch alongside the bronchial tree.
Region-
SystemRespiratory System
The pulmonary arteries are the major vessels that carry deoxygenated blood from the right side of the heart to the lungs. They form the arterial component of the pulmonary circulation, a low-pressure vascular circuit specialized for transporting blood to pulmonary capillary beds where gas exchange occurs.
\nThe pulmonary arterial pathway begins with the pulmonary trunk, which arises from the right ventricle. It divides into the right pulmonary artery and left pulmonary artery. Each enters the corresponding lung and branches extensively alongside the bronchial tree.
\n\nPulmonary Circulation
\nPulmonary circulation transports blood between the heart and lungs. Deoxygenated blood passes from the right ventricle through the pulmonary valve into the pulmonary trunk, then through progressively smaller pulmonary arteries to the alveolar capillaries.
\nAfter gas exchange, oxygenated blood returns to the left atrium through the pulmonary veins.
\n\nGeneral Pathway
\n- Right ventricle
- Pulmonary valve
- Pulmonary trunk
- Right and left pulmonary arteries
- Lobar pulmonary arteries
- Segmental pulmonary arteries
- Smaller intrapulmonary arteries
- Pulmonary arterioles
- Pulmonary capillaries
Pulmonary Trunk
\nThe pulmonary trunk arises from the right ventricle at the pulmonary orifice and carries the entire right ventricular output toward the lungs. Although it is an artery, it normally carries deoxygenated blood because arteries are defined by carrying blood away from the heart.
\n\nPulmonary Valve
\nThe pulmonary valve is a semilunar valve between the right ventricular outflow tract and pulmonary trunk. It prevents significant retrograde flow into the right ventricle during ventricular diastole.
\n\nCourse and Bifurcation
\nThe pulmonary trunk passes superiorly and posteriorly within the pericardial cavity. It initially lies anterior to the ascending aorta and divides into the right and left pulmonary arteries near the level of the sternal angle, approximately at the T4 to T5 vertebral level.
\n\nRight and Left Pulmonary Arteries
\n| Feature | Right Pulmonary Artery | Left Pulmonary Artery |
|---|---|---|
| Destination | Right lung | Left lung |
| Relative length | Longer | Shorter |
| Mediastinal relationship | Passes posterior to ascending aorta and superior vena cava | Passes beneath the aortic arch |
| Relationship to bronchus | Generally anterior | Superior |
Right Pulmonary Artery
\nThe right pulmonary artery is longer than the left. It passes horizontally toward the right lung, posterior to the ascending aorta and superior vena cava. At the right lung root, the superior lobar bronchus lies above the artery, while the bronchus intermedius lies posterior to it.
\nWithin the right lung, its branches supply the superior, middle, and inferior lobes before dividing into segmental pulmonary arteries.
\n\nLeft Pulmonary Artery
\nThe left pulmonary artery is shorter and passes toward the left lung beneath the aortic arch. At the left lung root, it lies superior to the left main bronchus and then divides into branches supplying the superior and inferior lobes.
\n\nRALS Relationship
\nThe relationship of the pulmonary arteries to the main bronchi is commonly remembered using RALS:
\n- Right pulmonary artery is Anterior to the bronchus.
- Left pulmonary artery is Superior to the bronchus.
Ligamentum Arteriosum
\nThe ligamentum arteriosum is a fibrous remnant of the fetal ductus arteriosus. It extends between the region of the left pulmonary artery and the inferior aspect of the aortic arch.
\n\nIntrapulmonary Branches
\nAfter entering the lungs, pulmonary arteries branch in close association with the bronchial tree. Lobar arteries accompany lobar bronchi, and segmental pulmonary arteries accompany segmental bronchi into bronchopulmonary segments.
\n\nBronchopulmonary Segments
\nA bronchopulmonary segment is an anatomically distinct subdivision of a pulmonary lobe supplied centrally by a segmental bronchus and a segmental branch of the pulmonary artery. Pulmonary veins generally run in intersegmental planes.
\n\nPulmonary Arterioles and Capillaries
\nSmaller pulmonary arterial branches become pulmonary arterioles and eventually supply dense capillary networks within the interalveolar septa. These capillaries lie extremely close to alveolar air and participate directly in gas exchange.
\n\nGas Exchange
\nBlood arriving through the pulmonary arterial system has relatively low oxygen and high carbon dioxide concentrations. Oxygen diffuses from alveolar gas into pulmonary capillary blood, while carbon dioxide diffuses from blood into the alveoli.
Published on October 17, 2026
Last updated on October 17, 2026
Last updated on October 17, 2026