The pulmonary artery is the only artery in the human adult which carries deoxygenated blood. All other arteries carry oxygenated blood. The pulmonary artery originates from the right ventricle of the heart through an opening which is guarded by the pulmonary valve.
The pulmonary valve is a non return valve which allows the blood to flow from the right ventricle to the pulmonary artery only. The pulmonary artery is enclosed in the pericardium of the heart.
The Pulmonary Arteries
The pulmonary artery branches into two pulmonary arteries: the left pulmonary artery and the right pulmonary artery – each going to the respective lung.
The right pulmonary artery is longer of the two. It crosses the upper part of the chest and passes below the arch of the aorta to enter the hilum of the right lung.
The left pulmonary artery is shorter and pierces the pericardium of the heart to enter the left lung.
Picture of pulmonary artery and heart.
Function of the Pulmonary Artery
The blood which comes from the various parts of the body is deoxygenated and carries metabolic waste. This blood needs to be got rid off the carbon dioxide it is carrying and replaced with oxygen so that it can keep on supplying oxygen to various parts of the body.
This exchange of gases is done in the alveoli of lung parenchyma. The left pulmonary artery carries deoxygenated blood to the left lung and the right pulmonary artery carries it to the right lung. In the lungs, the carbon dioxide from the blood is exchanged with the oxygen in the inhaled air. The carbon dioxide is then thrown out through the exhaled air.
Dimensions of the Pulmonary Artery
The pulmonary artery also called the pulmonary trunk at its beginning is 5 cms in length (2 inches) and 3 cms (1.2 inches) in diameter.
Pulmonary Arterial Pressure
The pulmonary artery pressures are lower than those in the aorta and vary during ventricular systole and diastole. During the ventricular systole (ventricular contraction) the pressure in the pulmonary artery is 26 mm of Hg. During ventricular diastole (ventricular relaxation) the pressure in the pulmonary artery is 10 mm of Hg.
Anatomy and Relations
As mentioned above, the whole pulmonary artery is enclosed with the ascending aorta in the visceral layer of the pericardial sac of the heart.
In front of the pulmonary artery lies pericardium, the pleura and the left lung. On either side is the auricle of the corresponding atrium. The left coronary artery passes behind the pulmonary artery. The cardiac plexus (which innervates the heart) lies above the point of its bifurcation and the arch of the aorta.
Pulmonary Artery Disease
Primarily there are two types of pulmonary artery disease.
- Pulmonary artery hypertension which is associated with high blood pressure in the pulmonary artery. This is particularly damaging to the heart and the liver.
- Pulmonary embolism is a dislodged thrombus which travels through the veins and gets lodged in the lungs. These emboli are dislodged from usually the legs and get lodged in the lungs. This disrupts the pulmonary circulation and is usually fatal.