<P> The left lung is divided into two lobes, an upper and a lower, by the oblique fissure, which extends from the costal to the mediastinal surface of the lung both above and below the hilum . The left lung, unlike the right, does not have a middle lobe, though it does have a homologous feature, a projection of the upper lobe termed the "lingula". Its name means "little tongue". The lingula on the left serves as an anatomic parallel to the right middle lobe, with both areas being predisposed to similar infections and anatomic complications . There are two bronchopulmonary segments of the lingula: superior and inferior . </P> <P> The mediastinal surface of the left lung has a large cardiac impression where the heart sits . This is deeper and larger than that on the right lung, at which level the heart projects to the left . </P> <P> On the same surface, immediately above the hilum, is a well - marked curved groove for the aortic arch, and a groove below it for the descending aorta . The left subclavian artery, a branch off the aortic arch, sits in a groove from the arch to near the apex of the lung . A shallower groove in front of the artery and near the edge of the lung, lodges the left brachiocephalic vein . The esophagus may sit in a wider shallow impression at the base of the lung . </P> <P> The lungs are part of the lower respiratory tract, and accommodate the bronchial airways when they branch from the trachea . The lungs include the bronchial airways that terminate in alveoli, the lung tissue in between, and veins, arteries, nerves and lymphatic vessels . The trachea and bronchi have plexuses of lymph capillaries in their mucosa and submucosa . The smaller bronchi have a single layer and they are absent in the alveoli . </P>

What is the surface area of a human lung