The lung is a paired organ that's necessary for respiration. In the lung, oxygen is extracted from the inhaled air, and carbon dioxide, the end product of the metabolism, is secreted.Key:
Humans have two lungs that are located inside the thoracic cavity and are separated by the mediastinum. The left lung can be divided into two, the right lung into three lobes. The lobes can be further subdivided into bronchopulmonary segments, each supplied by its own segmental bronchus and segmental artery. The right lung contains 10, the left lung 9 segments. There are 19 segments altogether in both lungs.The lungs originate at the hila, lateral to the trachea. The trachea itself bifurcates into the two main bronchi. These enter the hila together with the pulmonary arteries and veins. The main bronchus forms the root of the bronchial tree, branching several times into smaller and smaller bronchi, then bronchioli, and finally alveoli.The trachea and bronchi are kept open by cartilaginous rings. The walls of the bronchioli contain only patches of cartilage. There is no cartilage in the walls of the alveoli. They are prevented from collapse by surfactant.On the outside, the lung is covered by the visceral pleura. The transition from visceral to parietal pleura occurs at the hilum. The pleural fold inferior to the hilum is called the pulmonary ligament.Author of the picture: Rastrojo