The Anatomy of the Pulmonary Artery

How blood returns to the lungs to pick up oxygen

The main pulmonary artery, also called the pulmonary trunk, is a vessel that emerges from the heart. It divides into the left and right pulmonary arteries, which carry blood with relatively low oxygen content and high carbon dioxide content into the lungs. There, it is replenished with inhaled oxygen and excess carbon dioxide is "dropped off" to be released from the body via exhalation.

Heart pulmonary artery
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Anatomy

The pulmonary trunk and the left and right pulmonary arteries are relatively large arteries. They are each shaped like tubes with a lumen (the opening through which blood flows). The left and right pulmonary arteries send blood to the left and right lungs, respectively.

Structure

The pulmonary trunk and the right and left pulmonary arteries are shaped somewhat like a capital letter "T", with the trunk forming the lower portion and the left and right branches each forming one of the two sides at the top.

There is a valve between the right ventricle of the heart and the pulmonary trunk. This valve, which is composed of two cusps of connective tissue, is structured to open when the heart pumps so the blood can flow from the right ventricle to the pulmonary trunk. As the heart muscle relaxes, the valves close to prevent blood from flowing backward to the heart.

As with all arteries, the walls of the pulmonary arteries have several layers of muscle that allow them to dilate (widen) and constrict (become narrow). This is very different from the walls of veins, which are thinner and less muscular.

Most arteries in the body carry oxygenated blood, but the pulmonary arteries one of two exceptions that instead carry deoxygenated blood. (The umbilical arteries, which carry blood in need of oxygen from a developing baby to the mother, are the other.)

Location

The pulmonary trunk, which is relatively short and wide, 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.

These vessels pierce through the pericardium, which is the connective tissue lining around the heart. Because the heart is on the left side of the chest, the left pulmonary artery is closer to the lung than the right pulmonary artery.

After the left pulmonary artery enters the left lung, it divides into smaller branches.

The right pulmonary artery courses across the upper chest to enter the right lung. After this point, this artery divides into smaller branches.

Anatomic Variations

Generally, each pulmonary artery divides into three to seven branches. The most common anatomic variations of the pulmonary arteries are variations in the number of arterial branches in the lungs. And sometimes, one or more divisions can branch 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 is a condition in which the pulmonary valve does not open properly, resulting in diminished blood flow from the heart to the lungs. Symptoms, such as rapid breathing and slow childhood growth, can vary depending on the extent of the anatomical malformation. This defect is treated surgically.
  • Pulmonary artery stenosis: This congenital defect is characterized by a narrow pulmonary artery. It can be associated with a variety of heart defects and cause fatigue and shortness of breath, as well as symptoms of any such co-existing heart defects. Surgical repair may involve widening the artery with a stent.
  • Pulmonary artery sling: This is a congenital defect in which the left pulmonary artery branches off the right pulmonary artery, rather than directly from the pulmonary trunk. The defect is associated with narrowing of the trachea (windpipe) and bronchi (airways). Pulmonary artery sling can be treated surgically.

Function

The pulmonary arteries are part of the pulmonary circulation, which also includes pulmonary veins and pulmonary capillaries. The purpose of the pulmonary circulation is to transfer oxygen and carbon dioxide between the blood in the body and the air that's inhaled and exhaled in the lungs.

The specific 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 this exchange takes place.

When the blood is enriched with oxygen and cleared of carbon dioxide waste, it flows back through your pulmonary veins to your heart's right ventricle. From there, the blood is pumped to the left ventricle and finally dispersed through the aorta to the arteries that carry the oxygen-rich blood throughout the body. 

Clinical Significance

There are two main conditions that affect the pulmonary arteries in adults—pulmonary embolus (PE) and pulmonary arterial hypertension. Pulmonary arterial hypertension is a rare disease that develops over time. A PE is a blood clot in an artery of the lungs, and it is a medical emergency.

Pulmonary Embolus

A PE is a condition in which a blood clot lodges in the pulmonary artery, blocking blood flow to the lungs. Symptoms include:

  • Sudden shortness of breath
  • Pain in the chest and back
  • Cough
  • Bloody sputum
  • Excessive sweating
  • Lightheadedness
  • Blue lips or nails
  • Loss of consciousness

A PE can occur when a blood clot forms in a vein (such as in the legs) and travels through the heart, eventually becoming lodged in a pulmonary artery. Risk factors include blood clotting disorders, cancer, and prolonged physical immobility.


A pulmonary embolism is a life-threatening medical emergency that must be treated with blood thinners or an interventional procedure.

Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a rare type of pulmonary hypertension characterized by narrowing, stiffening, and thickening of the arteries in and around the lungs. It can cause fatigue, shortness of breath, hemoptysis (coughing up blood), and leg swelling.

Pulmonary arterial hypertension can develop without a known reason, and risk factors include scleroderma or other connective tissue diseases, toxin exposure, and liver cirrhosis.

The condition is progressive and may result in severe heart failure and disability due to intolerance of physical activity. Prescription medications can slow the progression of pulmonary arterial hypertension.

A Word From Verywell

The pulmonary arteries carry blood from your heart to your lungs. These vessels are part of the pulmonary circulation, and they are affected by and have an effect on other blood vessels in this system. Congenital deformities of the heart can be associated with variations in the pulmonary arteries, and these issues may require surgical repair during childhood.

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