Pulmonary trunk

At a glance

English

Pulmonary trunk

Latin (TA2)

Truncus pulmonalis

System

Artery

Region

Trunk

Side

Single, on the midline

About the pulmonary trunk

The pulmonary trunk, or main pulmonary artery, is the first vessel of the pulmonary circulation. It carries blood low in oxygen, returned from the body to the right heart, out of the right ventricle towards the lungs, where it is reoxygenated. It is unusual among arteries in carrying venous blood. It is short and broad, roughly 5 cm long and 3 cm across in adults.

It begins at the top of the conus arteriosus, the smooth outflow funnel of the right ventricle, at a circular opening guarded by the three cusps of the pulmonary valve. This opening lies higher than the right atrioventricular orifice and to its left. From there the trunk runs upwards and backwards, first in front of and then to the left of the ascending aorta, wrapped with it in a shared sleeve of serous pericardium. Under the concavity of the aortic arch, at about the level of the fifth thoracic vertebra, it divides into the right and left pulmonary arteries.

The right pulmonary artery is the longer; it runs horizontally across the mediastinum behind the ascending aorta and superior vena cava to the right lung. The left one is shorter and crosses anterior to the descending aorta on its way to the left lung. At the division the ligamentum arteriosum joins the start of the left pulmonary artery to the underside of the arch. Before birth this was the ductus arteriosus, which let blood bypass the lungs. Beyond the hilum the arteries branch with the airways into lobar, segmental and finer branches down to the arterioles round the alveoli. The lung tissue itself is fed separately by the bronchial arteries.

Pressure in the trunk is normally low and can be measured with a catheter passed through the right heart. A raised mean pressure is called pulmonary hypertension and may follow left heart failure, mitral valve narrowing, chronic lung disease or repeated clots; on CT the trunk then looks widened. A clot from the deep leg veins can lodge at the division and straddle both branches as a saddle embolus. In development the trunk forms when the truncus arteriosus divides into aorta and pulmonary trunk.

Course and supply

Arises from

Begins at the pulmonary valve at the top of the conus arteriosus of the right ventricle.

Ends in

Divides under the aortic arch, at about the fifth thoracic vertebra, into the right and left pulmonary arteries.

Supplies

Takes blood poor in oxygen from the right ventricle to both lungs, where gas exchange occurs.