Background: The lungs incorporate the parenchyma, vasculature, bronchial tree (trachea, bronchi, and bronchioles), and a network of investing connective tissue that supports and connects the structures to one another. The human lungs are a pair of large spongy organs for gas exchange between blood and the air. The lungs are covered by a serous membrane called the visceral pleura, and the surrounding cavity formed between the lungs and the surrounding chest wall and mediastinum, covered by parietal pleura, is called the pleural cavity. The lung roots formed by the structures which enter and emerge at the hilum, they are situated at vertebral levels T5-T7. The root of each lung is a short tubular collection of structures that together attach the lung to mediastinal structures. It is covered by a sleeve of mediastinal pleura that reflects onto the surface of the lung as visceral pleura. The region outlined by this pleural reflection on the medial surface of the lung is the hilum, where structures enter and leave. Within each root and located in the hilum are a pulmonary artery, two pulmonary veins, a main bronchus, bronchial vessels, nerves, and lymphatics.