How blood returns to the lungs to pick up oxygen
By Craig O. Weber, MD
Updated on June 28, 2023
Medically reviewed by Anisha Shah, MD
The pulmonary arteries are the two major arteries coming from right ventricle of your heart. Their job is to carry low-oxygen blood from the heart to the lungs. There, the blood is enriched with oxygen (oxygenation), and excess carbon dioxide is removed. The blood is then pumped back into the heart via the pulmonary veins.
This article will go over what the pulmonary arteries are and their function. It also covers medical conditions linked to the pulmonary arteries.
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The Anatomy of the Lungs
Anatomy of the Pulmonary Artery
The pulmonary artery is big, relatively short, and wide. The left and right pulmonary arteries are each shaped like tubes with an opening called a lumen that blood can flow through.
The left and right pulmonary arteries send blood to the left and right lungs, respectively.
How the Pulmonary Artery Is Structured
The pulmonary artery is shaped like the capital letter "T." The pulmonary trunk makes up the lower portion and the left and right pulmonary arteries each form one of the two sides at the top.
There is a valve between the right ventricle of the heart and the pulmonary artery. This valve has two cusps of connective tissue.
The valve is set up to open when the heart pumps and the blood can flow from the right ventricle to the pulmonary trunk. When the heart muscle relaxes, the valves close to prevent blood from flowing backward.
As with all arteries, the walls of the pulmonary arteries have several layers of muscle that allow them to widen (dilate) and narrow (constrict). This is very different from the walls of veins, which are thinner and less muscular.
The Four Valves of the Heart
Where Is the Pulmonary Artery in the Body?
The pulmonary artery is located at the exit of the right ventricle. This main arterial branch is located above the heart to the left of the ascending aorta.
The right pulmonary artery wedges in the aortic arch, behind the ascending aorta and in front of the descending aorta. The left pulmonary artery extends near the left side of the aorta.1
These vessels go through the connective tissue covering around the heart (pericardium). Since the heart is on the left side of the chest, the left pulmonary artery is closer to the lung than the right pulmonary artery is.
Once the left pulmonary artery enters the left lung, it splits into smaller branches. The right pulmonary artery goes across the upper chest and enters the right lung. From there, the artery divides into smaller branches.
How Blood Flows Through Your Heart and Lungs
What Does the Pulmonary Artery Do?
The pulmonary arteries are key players in pulmonary circulation along with the pulmonary veins and pulmonary capillaries.
Pulmonary circulation involves transferring oxygen and carbon dioxide between the blood in the body and the air that's inhaled and exhaled in the lungs.
The role of the pulmonary arteries is to carry blood that's low in oxygen and high in carbon dioxide waste to the pulmonary capillaries of the lungs, where the exchange takes place.
Most arteries in the body carry oxygenated blood, but the pulmonary arteries carry deoxygenated blood.
When the blood is enriched with oxygen and cleared of carbon dioxide waste, it flows back through the pulmonary veins to the heart's left atrium.
From there, the blood travels to the left ventricle and finally disperses through the aorta to the arteries that carry the oxygen-rich blood throughout the body.
Each pulmonary artery will usually divide into three to seven branches. The most common anatomic variations of the pulmonary arteries are related to the number of arterial branches in the lungs.2
How Much Oxygen Is In Your Blood?
Anatomic Variations of the Pulmonary Artery
Sometimes, one or branches split off before the right or left pulmonary artery enters the heart.
There are also some rare congenital deformities of the pulmonary arteries:
Pulmonary atresia: This condition is when the pulmonary valve does not open properly, which leads to diminished blood flow from the heart to the lungs. The symptoms of pulmonary atresia include rapid breathing and slow childhood growth but can vary depending on how severe the malformation is.3 The condition can be treated with surgery.
Pulmonary artery stenosis: This congenital defect causes a narrow pulmonary artery. It can be associated with other heart defects and cause symptoms like fatigue and shortness of breath. Surgical repair can widen the artery with a stent.
Pulmonary artery sling: This congenital defect occurs when the left pulmonary artery branches off the right pulmonary artery instead of directly from the pulmonary trunk. The defect is associated with the narrowing of the trachea (windpipe) and bronchi (airways).4 A pulmonary artery sling can be treated surgically.
What Diseases Are Linked to the Pulmonary Artery?
There are two main conditions that affect the pulmonary arteries in adults: pulmonary embolus (PE) and pulmonary arterial hypertension.
A pulmonary embolus is a blood clot in an artery of the lungs and is a medical emergency. Pulmonary arterial hypertension is a rare disease that develops over time.
Pulmonary Embolus
A pulmonary embolus (PE) is when a blood clot gets stuck in the pulmonary artery and blocks blood flow to the lungs.
A PE can occur when a blood clot forms in a vein somewhere in the body (often the legs) and travels through the heart where it gets stuck in a pulmonary artery. There are risk factors for developing a PE, including blood clotting disorders, cancer, and prolonged physical immobility.
Symptoms of a PE include:
Sudden shortness of breath
Pain in the chest and back
Cough
Coughing up blood (bloody sputum)
Excessive sweating
Lightheadedness
Blue lips or nails
Loss of consciousness5
When to Seek Medical Help
A PE is a potentially life-threatening medical emergency. If you have risk factors for and symptoms of a PE, you need immediate medical attention. Without treatment with blood thinning medication or procedures to get rid of the clot, a PE can be fatal.
What Happens If You Have a PE?
Pulmonary Arterial Hypertension
Pulmonary arterial hypertension is a rare type of pulmonary hypertension (high blood pressure) that causes narrowing, stiffening, and thickening of the arteries in and around the lungs.
The symptoms of pulmonary arterial hypertension include fatigue, shortness of breath, coughing up blood, and leg swelling.
There are certain risk factors for pulmonary arterial hypertension, including scleroderma or other connective tissue diseases, toxin exposure, and liver cirrhosis. However, some people get this kind of hypertension without a known reason.
Pulmonary arterial hypertension is progressive and can lead to severe heart failure and disability when a person becomes unable to tolerate physical activity.6 However, prescription medications can slow the progression of the condition.
How Is Pulmonary Hypertension Treated?
Summary
The pulmonary artery is a blood vessel that comes out of your heart. It splits into two sides, right and left, that carry blood to your lungs where oxygen and carbon dioxide are exchanged.
There are some conditions related to the pulmonary artery, including malformations that you're born with or diseases that come on later in life, like pulmonary arterial hypertension.
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