Pulmonary Trunk
The pulmonary trunk is a major artery that carries deoxygenated blood from the heart to the lungs, playing a key role in pulmonary circulation.
Pulmonary Trunk
Definition and Overview
Pulmonary Trunk is a large arterial vessel that originates from the right ventricle of the heart and serves as the primary conduit for deoxygenated blood traveling from the heart to the lungs. It is a short, wide vessel that soon divides into the right and left pulmonary arteries, which carry blood to the corresponding lungs for oxygenation.
Origin and Beginning
The pulmonary trunk arises from the conus arteriosus (infundibulum) of the right ventricle of the heart. It begins at the level of the upper border of the heart's right ventricle, immediately after the pulmonary valve.
Course and Direction
After its origin, the pulmonary trunk ascends obliquely upwards, backwards, and to the left. Its path is short—approximately 5 cm in length and 3 cm in diameter in adults.
Anatomical Relations
Relation to Ascending Aorta
As it ascends, the pulmonary trunk lies anterior and slightly to the left of the ascending aorta. At higher levels, the ascending aorta gradually becomes more medial and then rightward relative to the pulmonary trunk.
Relation to Left Auricle
The trunk passes in front of and slightly below the left auricle (left atrial appendage), with the left auricle partially covering its posterior left aspect.
Pericardial Coverage
The pulmonary trunk is almost completely enclosed within the pericardial sac, being covered by the visceral layer of serous pericardium except at its bifurcation, which lies just outside the pericardial reflection.
Bifurcation and Pulmonary Arteries
At the level of the sternal angle (junction of the manubrium and body of the sternum, corresponding to the intervertebral disc between T4 and T5 vertebrae), the pulmonary trunk bifurcates into the right and left pulmonary arteries.
The right pulmonary artery passes horizontally to the right, behind the ascending aorta and the superior vena cava. The left pulmonary artery passes horizontally to the left, in front of the descending aorta and left bronchus.
Level and Orientation of Bifurcation
The bifurcation of the pulmonary trunk occurs at the level of the sternal angle, which is at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae. The right and left pulmonary arteries diverge laterally, with the right passing posterior to the ascending aorta and superior vena cava, and the left passing anterior to the descending aorta.
Relation to Arch of Aorta
The concavity of the aortic arch lies superior to the bifurcation of the pulmonary trunk. The left pulmonary artery passes underneath the arch of the aorta, and the ligamentum arteriosum (a remnant of the fetal ductus arteriosus) connects the inferior surface of the aortic arch to the left pulmonary artery, near its origin from the pulmonary trunk.
Pulmonary Root Anatomy (Deferral)
Detailed anatomy of the pulmonary root, including the precise relationships of the pulmonary trunk with the pulmonary valve, right ventricular outflow tract, and nearby nerves and vessels, is typically described in advanced discussions of cardiac root structures.
Summary Table: Key Features of the Pulmonary Trunk
| Feature | Description |
|---|---|
| Origin | Right ventricle, at conus arteriosus (infundibulum) |
| Direction | Upwards, backwards, and leftwards |
| Length (adult) | ~5 cm |
| Diameter (adult) | ~3 cm |
| Pericardial coverage | Almost entirely within pericardial sac |
| Relation to aorta | Anterior and left of ascending aorta at first |
| Relation to left auricle | Anterior and below, left auricle posterior |
| Bifurcation | At sternal angle (T4/T5 disc), into R/L pulmonary arteries |
| Right pulmonary artery | Passes right, behind aorta and SVC |
| Left pulmonary artery | Passes left, in front of descending aorta, under aortic arch |
| Ligamentum arteriosum | From aortic arch to left pulmonary artery |
Clinical Relevance
The pulmonary trunk is critical in cardiopulmonary physiology, as it is the only vessel conveying all right ventricular output to the lungs. Disorders such as pulmonary hypertension, congenital anomalies (e.g., transposition of the great arteries, truncus arteriosus), and trauma can involve the pulmonary trunk or its branches. The close anatomical relationships with the aorta, left auricle, and pericardium are important in cardiac and thoracic surgery.
Key Points
- The pulmonary trunk is the main artery carrying deoxygenated blood from the right ventricle to the lungs.
- It begins at the right ventricle, ascends, and bifurcates at the sternal angle into right and left pulmonary arteries.
- Closely related to the ascending aorta, left auricle, and pericardium.
- The bifurcation occurs just beneath the concavity of the aortic arch.