The pulmonary trunk channels blood from the heart to the lungs. It is part of the circulatory system, involved in blood oxygenation.
Where the Pulmonary Trunk Resides
The pulmonary trunk originates from the right ventricle of the heart, the lower right chamber. It emerges from the conus arteriosus, guarded by the pulmonary valve at its base. This large, short artery typically measures about 5 centimeters (2 inches) in length and approximately 2 to 3 centimeters (0.8 to 1.2 inches) in diameter.
It initially lies anterior to the ascending aorta, then curves posteriorly and to the left. The entire pulmonary trunk is enclosed within the pericardial sac, the protective membrane surrounding the heart. This single vessel divides into two main branches: the left pulmonary artery, which extends to the left lung, and the right pulmonary artery, which travels to the right lung.
Its Essential Function
The pulmonary trunk transports deoxygenated blood away from the heart. This blood, which has circulated throughout the body and delivered its oxygen, is rich in carbon dioxide and low in oxygen. It acts as the initial conduit for this blood, directing it towards the lungs. It is the only artery in the adult human body that carries blood lacking a full oxygen supply.
The Pulmonary Trunk’s Place in Circulation
The pulmonary trunk is part of the pulmonary circulation, which moves blood between the heart and lungs. Deoxygenated blood, having returned from the body’s tissues to the heart’s right atrium, moves into the right ventricle. From there, the right ventricle pumps this blood into the pulmonary trunk.
Once the pulmonary trunk bifurcates, the right and left pulmonary arteries carry this deoxygenated blood into the respective lungs. Within the lungs, these arteries branch into progressively smaller vessels, eventually leading to tiny capillaries surrounding air sacs called alveoli. At this microscopic level, carbon dioxide is released from the blood into the alveoli to be exhaled, and oxygen from inhaled air is absorbed into the bloodstream. This newly oxygenated blood then collects in small veins, which merge to form larger pulmonary veins. These pulmonary veins then carry the oxygen-rich blood back to the left atrium of the heart, completing the pulmonary circuit and preparing the blood for distribution to the rest of the body.