The pulmonary veins drain oxygenated blood from the lungs into the left atrium. They emerge from the hila of the lungs, usually two veins from each lung, two left and two right ones. However, sometimes their number could vary from 3 to 5 in some individuals. A superior pulmonary and an inferior pulmonary vein can be distinguished in each pair. On arising from the hilum of lung, all the veins run transversely to the left atrium and enter its posterolateral portion.
The right pulmonary veins are longer than the left and lie inferiorly to the right pulmonary artery, behind the superior vena cava, right atrium, and ascending aorta. The left pulmonary veins, on the other hand, pass in front of the aorta. The pulmonary veins from the left lung are lobar veins; it means that each drain a single lobe with their corresponding name.
The hilum of lobe, like the hila of lungs, is an anatomical depression whose shape and depth vary with each individual. The hilum of lung may have the appearance of a hemispheric pit. The hila of the lobes are often round or oval. The hila of individual lobes are components of the hilum of lung.
Below, posterior aspect of human heart, showing the pulmonary veins that carry oxygenated blood from the lungs to left atrium, and the ordinary veins that drain the myocardium.
