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Bronchial tree and alveoli

Learning objectives 

This study unit will help you to:

  1. Name the main anatomical structures that comprise the bronchial tree. 
  2. Master the branching of the bronchial tree. 
  3. Recognize and distinguish the main features of each part of the bronchial tree. 
  4. Identify and name the bronchopulmonary segments of the left and right lungs.

Watch video

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.

Take a quiz

Now that you have watched the video about the elements of the bronchial tree, test your knowledge with our quiz.

Or perhaps you would prefer to test yourself on the entire lungs? We’ve got you covered! Now you can create your own custom quiz and choose your own topics.

Browse atlas

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


Key points about the bronchial tree and alveoli
Definition Bronchial tree is a term used to describe the multiple bronchi that conduct air from the trachea to alveoli
Branching Main (primary) bronchi → lobar (secondary) bronchi → segmental (tertiary) bronchi → intrasegmental bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar duct → Alveolar sac → alveolus
Segmental bronchi/ bronchopulmonary segments Left lung:
Superior lobe
(apicoposterior segment (1,2), anterior segment (3), superior lingular segment (4), inferior lingular segment (5))
Inferior lobe
(superior segment (6), anteromedial basal segment (7,8), lateral basal segment (9), posterior basal segment (10))

Right lung
Superior lobe
(apical segment (1), posterior segment (2), anterior segment (3))
Middle lobe
(lateral segment (4), medial segment (5))
Inferior lobe
(superior segment (6), medial basal segment (7), anterior basal segment (8), lateral basal segment (9), posterior basal segment (10))
Function Airway conduction, protection against pathogens and debris

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