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 b ...
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 cir ...
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 t ...
s to the
heart
The heart is a muscular 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 carbon dioxide t ...
. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the
left atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two atr ...
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 atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two atr ...
. 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 bronchus. ...
.
The right main pulmonary veins (contains oxygenated blood) pass behind the
right atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two at ...
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
The descending thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the aortic arch. It is located within the posterior mediastinal cavity, but frequently bulges into the left pleural cavity. The descending thoracic ...
.
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 using a ...
.
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
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
, 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
* ...
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, tha ...
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 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
Anomalous pulmonary venous connection (or anomalous pulmonary venous drainage or anomalous pulmonary venous return) is a congenital defect of the pulmonary veins.
Total anomalous pulmonary venous connection
''Total anomalous pulmonary venous co ...
(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.
See also
References
External links
*
Illustration at infomat.net
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Veins of the torso