The pulmonary artery is an artery that carries deoxygenated blood from the heart to one of the two lungs. The two arteriae pulmonales are branches of the truncus pulmonalis, the pulmonary trunk that connects to the right ventricle of the heart. Sensuously, the two pulmonary arteries are referred to as the sinistra pulmonary artery for the left lung and the dextra pulmonary artery for the right lung.
What is the pulmonary artery?
The pulmonary artery, also called the pulmonary artery, is twofold in nature to carry blood from the heart to the left lung and to the right lung. The two arteriae pulmonales represent the two branches of the branching of the truncus pulmonalis (pulmonary trunk). The two pulmonary arteries are the only arteries in which deoxygenated blood is transported. They are appropriately called the arteria pulmonalis sinistra to supply the alveoli of the left lung and the arteria pulmonalis dextra to supply the right lung. The arteriae pulmonales open into the entrance port (hilus) of the respective lung. After entering the hilus, the pulmonary arteries branch further to the level of the capillaries that surround the alveoli, where metabolic exchange and oxygenation of the blood occurs. The two pulmonary arteries, together with the truncus pulmonalis, which connects to the right ventricle, form the arterial part of the pulmonary circulation or small circulation.
Anatomy and structure
The two arteriae pulmonales are the only two branches into which the truncus pulmonalis branches. The branching (bifurcatio trunci pulmonalis) occurs at the level of the fourth thoracic vertebra immediately below the aortic arch. The right pulmonary artery is, for anatomical reasons, slightly longer than the left and runs below the aortic arch to the right toward the pulmonary hilus, the entrance port of the right lung. In principle, the pulmonary arteries resemble the arteries of the systemic circulation in their anatomical structure. The walls of the pulmonary artery consist of three layers. From the inside out, these are the tunica intima, the tunica media, and the tunica adventitia. The tunica intima is composed of a single-layer endothelium and an adjoining layer of loose connective tissue and the final membrana elastica interna. The tunica media is only weakly developed in the pulmonary arteries. It consists of muscle cells that wind obliquely around the vessels and of elastic and collagen fibers. The tunica adventitia, which adjoins the tunica media on the outside, is practically the supply unit of the arteries and is composed mainly of collagenous and elastic connective tissue interspersed with fine vessels to supply the vessel walls and nerves to control vasoconstriction. However, the total vascular resistance in the pulmonary circulation is only about one-tenth that of the systemic circulation, and evolution has taken this into account in the anatomy of the individual layers of the vascular walls.
Function and Tasks
The main function of the arteriae pulmonales is to carry deoxygenated blood from the right ventricle to the two lobes of the lungs for the purpose of mass transfer and oxygenation. Because the blood that is directed into the lungs does not serve to supply the lungs but benefits other target tissues, practically the entire body metabolism, the pulmonary arteries are also called vasa publica. Oxygen exchange in the alveoli of the two lungs depends not least on the oxygen supply in the breathing air. If there is a lack of oxygen (hypoxia) in certain regions of the lungs, the partial hypoxia triggers vasoconstriction in the arteries located in the immediate vicinity. This means that the arterial vasculature of the lung is individually controlled with respect to vasoconstriction. For both arteriae pulmonales, this results in a negative task, namely, to respond as little as possible to sympathetic impulses for arterial vasoconstriction so as not to undermine the individual cross-sectional control of the arteries within the lung.
Diseases
In principle, dysfunction of the arteriae pulmonales may be acquired or caused by inherited genetic defects that lead to malformations of the pulmonary arteries from birth. Inherited malformations are often observed in association with other inherited cardiac defects.The range of pulmonary artery anomalies based on genetic defects is very wide and can lead to life-threatening conditions even in newborns in rare cases. An acquired or inherited disease with various causes is pulmonary hypertension (PH), which develops due to vasoconstriction of the pulmonary arteries. In many cases, no organic cause can be found for the occurrence of PH. The mechanisms for the development and progression of the disease are not yet fully understood. One of the causes is that the vessel walls react unusually strongly to messenger substances that are supposed to cause vasoconstriction, so that the vessels gradually become chronically constricted, leading to the typical clinical picture. Other causes are seen in inflammations within the vessel walls or in side effects of medications that lead to vessel wall thickening and provoke PH. Another disease that can only be indirectly related to the functioning of the pulmonary arteries is pulmonary embolism. It results from a thrombus or embolus, a blood clot that has formed and dislodged somewhere on the venous side of the systemic circulation. It then travels with the bloodstream through the right atrium into the right ventricle and is carried into the pulmonary circulation. Depending on its size, the thrombus then blocks one of the pulmonary arteries with potentially serious consequences, including acute danger of death.
