Difference Between Pulmonary Artery and Pulmonary Vein

Main Difference – Pulmonary Artery vs Pulmonary Vein

Many mammals have a double circulatory system by which the blood is circulated twice through the heart. The two circulatory systems are the pulmonary circulation and the systematic circulation. The pulmonary circulation is involved in exchanging gases, which are dissolved in the blood, with the external environment through lungs. Therefore, it makes a circuit between the heart and the lungs. Pulmonary artery and pulmonary vein are the two blood vessels found in pulmonary circulation. The main difference between pulmonary artery and pulmonary vein is that pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs whereas pulmonary vein carries the oxygenated blood from the lungs to the left atrium of the heart.

Key Areas Covered

1. What is Pulmonary Artery
      – Definition, Characteristics, Function
2. What is Pulmonary Vein
      – Definition, Characteristics, Function
3. What are the Similarities Between Pulmonary Artery and Pulmonary Vein
      – Outline of Common Features
4. What is the Difference Between Pulmonary Artery and Pulmonary Vein
      – Comparison of Key Differences

Key Terms: Deoxygenated Blood, Left Atrium, Lungs, Oxygenated Blood, Pulmonary Artery, Pulmonary Circulation, Pulmonary Vein, Right Ventricle

What is Pulmonary Artery

Pulmonary artery is the artery that carries deoxygenated blood from the right ventricle of the heart to the lungs. The major pulmonary artery that originates from the right ventricle of the heart is called the pulmonary trunk. At the level of fifth thoracic vertebra, the pulmonary artery divides into two; left pulmonary artery (LPA) and right pulmonary artery (RPA). The left pulmonary artery carries blood to the left lung while the right pulmonary artery carries blood to the right lung. The RPA, which is longer than the LPA, travels through the mediastinum and slightly slopes inferiorly to the hilus of the right lung.

Figure 1: Origination of the Pulmonary Blood Vessels from the Heart

Both RPA and LPA are further divided into segmental and subsegmental pulmonary arteries. These divisions are parallel to the segmental and subsegmental bronchi and run next to them. Therefore, the naming of the segmental and subsegmental pulmonary arteries can be done based on the bronchopulmonary segment they feed. The origination of the pulmonary blood vessels is shown in figure 1. 

What is Pulmonary Vein

Pulmonary vein is the vein that carries oxygenated blood from the lungs to the left atrium of the heart. A small amount of oxygenated blood is also carried to the heart by the bronchial veins. The major pulmonary vein divides into four pulmonary veins: right superior pulmonary vein, right inferior pulmonary vein, left superior pulmonary vein and left inferior pulmonary vein.

Figure 2: Division of Pulmonary Blood Vessels

Different Pulmonary Veins and Parts of the Lungs that Supply Blood to them

All pulmonary veins do not run along with the respective bronchi as pulmonary arteries do. The superior pulmonary veins run in the intersegmental septa while the inferior pulmonary veins run with the respective bronchi. The division of both pulmonary artery and pulmonary vein in the right lung is shown in figure 2.

Similarities Between Pulmonary Artery and Pulmonary Vein

• Pulmonary artery and pulmonary vein are the blood vessels in the pulmonary circulation.
• Both pulmonary artery and pulmonary vein carry blood between the heart and the lungs.
• Each pulmonary artery and vein form a network in each alveolus in the lungs.
• Both pulmonary artery and pulmonary vein are involved in the gas exchange between the blood and the external environment through the lungs.
• Pulmonary artery and pulmonary vein are exceptions of a typical artery and vein, respectively.

Difference Between Pulmonary Artery and Pulmonary Vein

Definition

Pulmonary Artery: Pulmonary artery is the artery that carries blood from the right ventricle of the heart to the lungs for the oxygenation.

Pulmonary Vein: Pulmonary vein is the vein that carries oxygenated blood from the lungs to the left atrium of the heart.

Direction of the Flow

Pulmonary Artery: Pulmonary artery carries blood from the left ventricle of the heart to lungs.

Pulmonary Vein: Pulmonary vein carries blood from the lungs to the right atrium of the heart.

Type of Blood

Pulmonary Artery: Pulmonary artery carries deoxygenated blood.

Pulmonary Vein: Pulmonary vein carries oxygenated blood.

Division

Pulmonary Artery: Pulmonary artery divides into two; each artery carries blood to each of the lungs.

Pulmonary Vein: Pulmonary vein divides into four; each pair of veins goes to each lung.

Direction of the Segmental and Subsegmental Parts

Pulmonary Artery: The segmental and subsegmental arteries of the pulmonary artery run next to the respective segmental and subsegmental bronchi of the lung.

Pulmonary Vein: The segmental and subsegmental arteries of the pulmonary vein run independently from the bronchi in the interlobular septa.

Anatomy of the Wall

Pulmonary Artery: Pulmonary artery wall is thick and elastic.

Pulmonary Vein: Pulmonary vein wall is thin when compared to the pulmonary artery.

Valves

Pulmonary Artery: Pulmonary artery consists of valves.

Pulmonary Vein: Pulmonary vein lacks valves.

Blood Pressure

Pulmonary Artery: Since pulmonary artery begins from a ventricle, the blood pressure in the pulmonary artery is high.

Pulmonary Vein: Since pulmonary vein begins from an atrium, the blood pressure inside the pulmonary vein is comparatively low.

Conclusion

Pulmonary artery and pulmonary vein are the two types of blood vessels found in the pulmonary circulation. The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs. The pulmonary vein carries oxygenated blood from the lungs to the left atrium of the heart. The main function of the pulmonary circulation is to exchange carbon dioxide and oxygen with the external environment through the lungs. The main difference between pulmonary artery and pulmonary vein is the type of blood they carry and the direction of the blood flow in each type of pulmonary blood vessel.

Reference:

1. Bailey, Regina. “What Is a Pulmonary Artery?” ThoughtCo, Available here. Accessed 29 Aug. 2017.
2. “Pulmonary Artery Anatomy.” CT Pulmonary Angiography, Available here. Accessed 29 Aug. 2017.
3. Knipe, Henry. “Pulmonary veins | Radiology Reference Article.” Radiopaedia.org, Available here. Accessed 29 Aug. 2017.

Image Courtesy:

1. “Blausen 0457 Heart SectionalAnatomy” By Blausen Medical Communications, Inc. (CC BY 3.0) via Commons Wikimedia
2. “Computed tomograph of pulmonary vessels” By Mikael Häggström (CC0) via Commons Wikimedia 

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