The pulmonary artery originates from the heart and serves as the beginning of the circulation pathway to the lungs. Unlike other arteries, it carries deoxygenated blood rather than oxygen-rich blood. This vessel is fundamental to the process of gas exchange, ensuring the body can refresh its blood supply with oxygen.
Detailed Anatomical Position
The pulmonary artery begins in the right ventricle, the lower right chamber of the heart. From this chamber, the vessel emerges as a single, wide structure known as the pulmonary trunk, or main pulmonary artery. It is positioned at the front of the heart, secured by the pulmonary valve. The pulmonary trunk travels upward and slightly backward, lying within the central compartment of the chest cavity, called the mediastinum.
This short, broad trunk divides beneath the arch of the aorta. This division forms the right pulmonary artery and the left pulmonary artery, which are the two main branches. The right artery extends toward the right lung, while the left artery extends toward the left lung.
Both branches enter the root of their respective lungs at the hilum. Once inside, the arteries divide repeatedly, becoming progressively smaller vessels. These smaller branches ultimately lead to a dense network of capillaries that surround the air sacs of the lungs.
Role in the Pulmonary Circuit
The pulmonary artery is part of the pulmonary circuit, the short loop of circulation between the heart and the lungs. Its primary function is to transport oxygen-poor blood away from the right side of the heart to the lungs for gas exchange. This blood, having circulated throughout the body, is saturated with carbon dioxide and low in oxygen.
In the lungs, the blood flows through the capillary beds where it releases carbon dioxide and absorbs oxygen from the inhaled air. This gas exchange is the defining function of the pulmonary circuit. Once oxygenated, the blood is collected by the pulmonary veins, which carry it back to the left side of the heart to be pumped out to the rest of the body in the systemic circuit.
Surrounding Structures and Connections
The pulmonary artery’s central location places it in contact with other major structures. The main pulmonary artery lies immediately adjacent to the ascending aorta, the largest artery in the body. The two vessels intertwine at the heart’s base. This close relationship is a defining feature of the great vessels emerging from the heart.
After the pulmonary trunk divides, the right and left pulmonary arteries relate closely to the main bronchi, the two large airways leading into the lungs. The right pulmonary artery travels in front of the right main bronchus as it enters the lung. Conversely, the left pulmonary artery passes superior to the left main bronchus. This proximity is important for understanding the placement of structures within the root of each lung.
The pulmonary artery shares a developmental connection with the aorta through the ligamentum arteriosum. In fetal life, this was the ductus arteriosus, a temporary blood vessel that allowed blood to bypass the non-functional lungs. After birth, it closes to form a fibrous cord connecting the left pulmonary artery to the aortic arch.
Clinical Implications of Location
The central location and specific function of the pulmonary artery make it susceptible to serious health conditions. One is a Pulmonary Embolism (PE), which occurs when a blood clot, often originating in the legs, travels through the right side of the heart and becomes lodged in the pulmonary artery or one of its branches. This blockage prevents blood flow to a section of the lung, impairing gas exchange and causing strain on the right ventricle.
Another condition is Pulmonary Hypertension (PH), characterized by abnormally high blood pressure within the pulmonary arteries. This elevated pressure is often caused by the narrowing or obstruction of small vessels within the lungs, forcing the right ventricle to work harder to push blood through the circuit. Because the pulmonary artery is sensitive to changes in pressure, its diameter often increases in patients with PH.
The main pulmonary artery lies between the right ventricle and the lungs, meaning issues like PH and PE directly cause stress on the heart muscle. Over time, this sustained strain can lead to right heart failure, which is a common consequence of conditions that affect the pulmonary artery. Physicians frequently measure the dimensions of the pulmonary artery using CT scans to screen for and monitor the severity of pulmonary hypertension.