The tracheobronchial tree from the carina to the respiratory bronchioles is supplied by bronchial arteries, branches of the descending aorta. The trachea is supplied by tracheal arteries, branches of the inferior thyroid artery and bronchial arteries. There are approximately 300 million alveoli in the lungs of normal young adults. As they contain alveoli, respiratory bronchioles are thus involved in both gas exchange and air transportation.įurther subdivision occurs beyond the respiratory bronchioles, to alveolar ducts and alveolar sacs. Lastly, alveoli are the single basic structural unit responsible for gas exchange in the lung.
Respiratory bronchioles contain numerous small thin-walled alveoli that bulge outwards from their lumens. Their function is to transport air to the most distal parts of the lungs where respiratory bronchioles are located. These structures lack cartilage and do not participate in gas exchange. Peripheral to the segmental bronchi there are 20 - 25 further branchings into conducting bronchioles, and finally terminal bronchioles.
Venous drainage occurs through intersegmental tributaries of the pulmonary veins, located in the interstitium between segments. Each bronchopulmonary segment is separated from adjacent segments by thin fibrous septa ( pulmonary interstitium) and is pyramidal-shaped with the apex of the pyramid facing the lung root and the base of the pyramid facing the pleural surface.īronchopulmonary segments are independently supplied by a single segmental bronchus and a tertiary branch of the pulmonary artery, which both enter the segment at its apex. At the level of the tertiary segmental bronchi, sections of lung called bronchopulmonary segments are defined that represent the largest subdivisions of a lobe can be surgically resectable, analogous to the segments of the liver.
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