Bronchi: What are they? Location, Structure, Anatomy, Function, Histology and Associated Conditions

They branch from the trachea and are the primary conduit for air to enter the lungs.

Each bronchus branches into smaller tubes or bronchioles.

Location, structure, and anatomy

The bronchi are found in the thoracic cavity, trachea, and lungs.

It originates in the lower end of the trachea, where it divides or bifurcates in the left and right bronchus.

Primary bronchi

There are two primaries (extrapulmonary) bronchi, the right and left main bronchi, that connect the trachea to the two lungs.

Right main bronchus (primary)

The branch that leads to the right lung is called the right primary bronchus. With about 2.5 cm in length, it is shorter than the left primary bronchus.

But of broader diameter. Enter the right lung around the fifth thoracic vertebra’s level.


Divisions and Anatomy

The right primary bronchi branch out into three secondary or lobar bronchi, the upper, middle, and lower lobe bronchi.

The right upper secondary bronchus is also known as the eparterial bronchus because it is the only bronchial tube that originates above the level of the pulmonary artery.

The bronchial lymph nodes are located at the point of origin of each lobar bronchi.

The main bronchus divides first in the right upper lobe bronchus and the intermediate bronchus, and the latter gives rise to the middle and lower bronchi.

The secondary bronchi are then subdivided into ten tertiary or segmental bronchi.

These tertiary bronchi give rise to the subsegmental bronchi, leading to the smaller branches of a bronchus, the bronchioles.

The azygos vein covers the right primary bronchus from behind, at the lung base.

Left main bronchus (primary)

The left primary bronchus supplies air to the left lung and is about 5 cm, twice as much as the right main bronchus.

It enters the left lung around the level of the sixth thoracic vertebra, passes under the aortic arch, and crosses the esophagus, the thoracic duct, and the descending aorta from the front.

Divisions and Anatomy

Like the right main bronchus, the left one also divides into two upper and lower lobar bronchi.

The lobar bronchi are subdivided into eight tertiary or segmental bronchi.

The tertiary bronchi divide into smaller tubes into subsegmental bronchi and bronchioles.

Anatomy of the bronchial wall

Like the trachea, the bronchi are also surrounded by cartilaginous rings in the form of C.

However, the smaller bronchial tubes have irregular cartilaginous laminae instead of rings to support them.

Together with a layer of smooth muscle bands, these cartilage structures control the diameter of the bronchial lumen during inhalation and exhalation.

Diagram of the anatomy of the bronchus

The internal walls (luminal surface) have a mucous membrane lining and hair-like projections called cilia that cover them.

Although not as many as in the trachea, the bronchial epithelium also has goblet cells that secrete mucus that protects the mucous lining.

Bronchial histology

The outer bronchial walls are covered by an adventitia band that connects the bronchi and the other tissues of the lungs.

Bronchial Function in the Respiratory System

What do the Primary Bronchuses do?

The primary function of the primary bronchi is to bring oxygen-rich air to the lungs during inhalation and allow the carbon-rich air to leave the lungs and reach the trachea on exiting during exhalation.

It is the connection between the rest of the respiratory tract and the lungs. Its cartilaginous walls help maintain its shape during breathing, preventing it from collapsing.

It prevents foreign particles (such as dust) from entering the lungs.

The smaller bronchi tubes are assigned to supply specific regions within the lungs.

What do the Secondary Bronchuses do?

The three secondary or lobar bronchi of the right lung act as air passage to the right lung’s upper, middle, and lower lobes.

There are only two secondary bronchi in the left lung since there are only two lobes to supply, the upper and lower lobes.

What do the Tertiary Bronchians do?

These supply air to the bronchopulmonary segments. There are ten bronchopulmonary segments in the right lung, so it has ten tertiary bronchi.

While the left lung has eight tertiary bronchi to attend each of its eight bronchopulmonary segments.

Subsegmental function

These tiny tubes are responsible for allowing the inhaled air to reach the alveoli through the bronchioles, where the exchange of oxygen and carbon dioxide occurs.

Associated health conditions

  • Bronchitis.
  •  Bronchial asthma .
  • Bronchiectasis
  • Broncoespasmo.