Bronchial Tree: Function, Anatomy, Structure, Infections and Associated Allergies

It is aptly named for its resemblance to the branches of a tree, as the longer tubes are perpetuated in small tubes in an intricate frame of branches.


Air circulates through the bronchial tree during respiration. It consists of bronchi, bronchioles, and alveoli.

Anatomy of the bronchial tree

Just around the level of the sternal angle, just behind the manubrium, the trachea divides into the right and left primary bronchi.

Around the lumen of each branch of the extension principle, cartilage rings keep the larger airways open as they branch into smaller tubes.

The right primary branch is at a more vertical angle, increasing the chances of foreign particles falling into the tubular formation.

Each beginning of the bronchi is secreted once more as it descends into the lungs, forming the lobar and then the segmental bronchi, also known as the secondary and tertiary bronchi, respectively.

From there, the network continues to branch out into smaller tubes known as bronchioles.

Structure of the bronchial tree


The bronchi are the main tube to the lungs. When someone breathes through the nose or mouth, the air travels to the larynx. The next step is through the windpipe, which carries air to the left and right bronchi.

The bronchi get smaller the closer they get to the lung tissue and are later considered bronchioles. These passageways then evolve into tiny air sacs called alveoli, which is the site of oxygen and carbon dioxide exchange in the respiratory system.

The primary bronchi are found in the upper portion of the lungs, with secondary bronchi near the center of the lungs. The tertiary bronchi are located near the bottom of these organs, just above the bronchioles.

There are no gas changes in any of the bronchi. When the bronchial tubes swell due to irritants or infection, bronchitis occurs and makes breathing difficult. Those with bronchitis also tend to have much more mucus and phlegm than someone without inflamed bronchial tubes .


Bronchioles are tubes in the lungs that branch off from the larger bronchi that enter each lung, from the large, unique windpipe that connects to the mouth.

As such, the bronchioles are one of the smallest airways in the respiratory tract, leading directly to the alveolar ducts that house the alveoli responsible for gas exchange with the blood.

Each bronchus, after entering the lung, divides into secondary and tertiary bronchi, which continually become small. Eventually, the bronchi transform into bronchioles as they lose some of the structural elements that define a bronchus. The bronchioles lack hyaline cartilage, which surrounds the bronchi and prevents them from collapsing.

The bronchioles are anchored to the tissues to which they carry air. The bronchioles also support the smooth muscle tissue, which surrounds each bronchiole. This smooth muscle tissue is sometimes prone to contracting, reducing the size of the bronchioles. This is known as bronchospasm and is seen in patients with asthma and other lung diseases.

The bronchioles continue to divide into smaller terminal bronchioles, which divide into the smaller respiratory bronchioles. In respiratory bronchioles, the alveoli begin to surround the bronchioles and the walls become thin enough for gas exchange to take place.


The alveoli are small ends of the alveolar ducts. These small air sacs work to exchange oxygen and carbon dioxide in the blood. Certain respiratory diseases cause a thickening of the walls of the alveoli, which restricts movement and causes breathing difficulties.

Infections or allergies

The tubular network within the lungs is actually divided into two basic sections. The air conduction network ends at the terminal bronchioles while the respiratory segment begins with the respiratory bronchioles.

The medical condition known as asthma is the result of an infection or an allergy. An asthma attack means that the smooth muscle of the respiratory bronchioles is spasming. The respiratory bronchioles are devoid of cartilage to keep the airways open, and therefore the airway contracts along with the muscle.