The pulmonary veins are the

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...

s that transfer

oxygenated blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the ci ...

from the

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...

s to the

heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...

. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary veins are part of the

pulmonary circulation The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lungs ...

Structure

There are four main pulmonary veins, two from each lung – an inferior and a superior main vein, emerging from each hilum. The main pulmonary veins receive blood from three or four feeding veins in each lung, and drain into the left atrium. The peripheral feeding veins do not follow the bronchial tree. They run between the pulmonary segments from which they drain the blood. At the root of the lung, the right superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the lung hilum. Behind the pulmonary artery is the

bronchus A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchu ...

. The right main pulmonary veins (contains oxygenated blood) pass behind the right atrium and

superior vena cava The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart. It is a large-diameter (24 mm) short length vein th ...

; the left in front of the descending thoracic aorta.

Variation

Occasionally the three lobar veins on the right side remain separate, and not infrequently the two left lobar veins end by a common opening into the left atrium. Therefore, the number of pulmonary veins opening into the left atrium can vary between three and five in the healthy

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction usi ...

. The two left lobar veins may be united as a single pulmonary vein in about 25% of people; the two right veins may be united in about 3%.

Function

The pulmonary veins play an essential role in respiration, by receiving blood that has been oxygenated in the

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

and returning it to the left atrium.

Clinical significance

As part of the pulmonary circulation they carry oxygenated blood back to the heart, as opposed to the veins of the

systemic circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...

which carry deoxygenated blood. On chest X-ray, the diameters of pulmonary veins increases from upper to lower lobes, from 3 mm at the first intercoastal space, to 6 mm just above the diaphragm. A rare

genetic defect A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorde ...

of the pulmonary veins can cause them to drain into the pulmonary circulation in whole or in part, this is known as a total anomalous pulmonary venous connection (or drainage), or partial anomalous pulmonary connection, respectively.

Additional images

File:Computed tomograph of pulmonary vessels.jpg, Computed tomography of a normal lung, with different levels of pulmonary veins. File:Bronchial anatomy.jpg, Bronchial anatomy File:Gray503.png, Transverse section of thorax, showing relations of pulmonary artery. File:Gray504.png, Pulmonary vessels, seen in a dorsal view of the heart and lungs.

References

External links

*
Illustration at infomat.net
{{Authority control Veins of the torso