Bronchial tree and alveoli

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Bronchial tree is the term used to describe the branching tubular structure conducting air between the trachea and the lungs. It comprises bronchi and bronchioles, which open into alveoli. Based on their size, function and histological structure, there are three types of bronchi including main (primary) bronchi, lobar (secondary) bronchi, segmental (tertiary) and intrasegmental bronchi. All bronchi have an outer layer containing variable amounts of irregularly placed cartilaginous plates.

Each tertiary bronchus supplies a bronchopulmonary segment of the lung. Bronchopulmonary segments are pyramidal shaped segments of the lung which are supplied by their own individual bronchus and artery. They are subsequently named according to the tertiary bronchi they are supplied by i.e. apical segmental bronchi supply the apical segment of the lung. Venous and lymphatic vessels of the bronchopulmonary segments do not extend into the segments but rather, pass through adjacent intersegmental planes (the intervening septae that separate each segment). 

Within each bronchopulmonary segment the tertiary bronchi branch into conducting bronchioles which eventually end as terminating bronchioles. Terminating bronchioles give rise to respiratory bronchioles that end in small sacs known as alveoli which form the site of gaseous exchange between the blood and the lungs. 

The main function of the bronchial tree is to provide a passageway for air to move into and out of each lung. In addition, the mucous membrane of these airways protects the lungs by capturing debris and pathogens. 

This video tutorial will provide you with an overview of the bronchi, bronchioles and alveoli.

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Browse atlas

Now you can observe each structure of the bronchial tree and alveoli in the image gallery below.

Summary