Pulmonary artery

Structure

In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide—approximately 5 centimetres (2.0 in) in length and 3 centimetres (1.2 in) in diameter. It then branches into two pulmonary arteries (left and right), which deliver deoxygenated blood to the corresponding lung.

Embryology

The pulmonary arteries originate from the truncus arteriosus and the sixth pharyngeal arch. The truncus arteriosis is a structure that forms during the development of the heart as a successor to the conus arteriosus.

By the third week of embryological life, the endocardial tubes have developed a swelling in the part closest to the heart. The swelling is known as the bulbus cordis and the upper part of this swelling develops into the truncus arteriosus The structure is ultimately mesodermal in origin. During development of the heart, the heart tissues undergo folding, and the truncus arteriosus is exposed to what will eventually be both the left and right ventricles. As a septum develops between the two ventricles of the heart, two bulges form on either side of the truncus arteriosus. These progressively enlarge until the trunk splits into the aorta and pulmonary arteries.

During embryological life, the ductus arteriosis connects the pulmonary trunk and the arch of aorta, allowing blood to bypass the lungs.

Function

The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The blood here passes through capillaries adjacent to alveoli and becomes oxygenated as part of the process of respiration.

In contrast to the pulmonary arteries, the bronchial arteries supply nutrition to the lungs themselves.

The pulmonary artery pressure (PA pressure) is a measure of the blood pressure found in the pulmonary artery. This is measured by inserting a catheter into the pulmonary artery. The mean pressure is typically 9 - 18 mmHg, and the wedge pressure measured in the left atrium may be 6-12mmHg. The wedge pressure may be elevated in left heart failure, mitral valve stenosis, and other conditions, such as sickle cell disease.

Clinical significance

The pulmonary artery is relevant in a number of clinical states. Pulmonary hypertension is used to describe an increase in the pressure of the pulmonary artery, and may be defined as a mean pulmonary artery pressure of greater than 25mmHg. This may occur as a result of heart problems such as heart failure, lung or airway disease such as COPD or scleroderma, or thromboembolic disease such as pulmonary embolism or emboli seen in sickle cell anaemia.

Pulmonary embolism refers to an embolus that lodges in the pulmonary circulation. This may arise from a deep venous thrombosis, especially after a period of immobility. A pulmonary embolus is a common cause of death in patients with cancer and stroke. A large pulmonary embolus affecting the pulmonary trunk is called a saddle embolus.