Pulmonary vein three and five in the healthy population. 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%. The pulmonary veins play an essential role in respiration, by receiving blood that has been oxygenated in the alveoli and returning it to the left atrium. As part of the pulmonary circulation they carry oxygenated blood back to the heart, as opposed to the veins of the systemic circulation which carry deoxygenated blood. A rare genetic defect of the pulmonary veins can cause them to
Azygos vein displaced laterally, thereby creating a pleural septum separating an azygos lobe from the upper lobe of the right lung. The anatomy of this blood vessel can be quite variable. In some rare variations for example, it also drains thoracic veins, bronchial veins and even gonadal veins. The vein is so named because it has no symmetrically equivalent vein on the left side of the body. The azygos system is considered to be the azygos vein located from rib number 2 to rib number 4 while the left part of the body has the hemiazygos vein and the accessory hemiazygos vein