How is lung tissue oxygenated?

Answer 1

When most people learn about circulation in the human body, they usually learn of only the two main types, pulmonic (in which blood goes to the lungs to obtain oxygen and release Carbon Dioxide) and, systemic (in which this oxygenated blood is sent through the aorta and out though the arterial system. This does leave an very important question unanswered indeed. Well, as you may have realised and correctly assumed, the lung parenchyma (basically its structure and tissues) cannot be perfused (receive blood supply) from the pulmonic circulation. It is perfused from the systemic circulation. Specifically, from two branches of the thoracic aorta known as bronchial arteries. The left bronchial artery to the left lung usually arises directly from the thoracic aorta, while the right one can also rise from the thoracic aorta, however, it usually either arises from the left bronchial artery, or from a common trunk off the thoracic aorta with the 3rd posterior intercostal artery. They enter the lung and divides into capillaries supplying its parenchyma. The venous return is a bit more complex. The bronchial veins return some, but not all of the used blood back to the heart via the vena azygos major on the right and the accesory hemiazygos vein on the right. As the bronichial veins does not drain all of the returning blood, it may be interesting to note the some of it gets directed into the pumonary system. and returns to the heart via the oxgenated pulmonary veins. You have asked a important question, that many laypeople have wondered but never really ask. I hope I have answered it in a meaningfull and relatively clear way. Note: a pretty good discussion on this can be found here: http://www.meridianinstitute.com/eamt/files/barber/Bar1CH2.htm