Tertiary (Segmental) Bronchi

1. Overview

The tertiary bronchi, also known as segmental bronchi, are subdivisions of the secondary (lobar) bronchi. Each tertiary bronchus supplies a specific, anatomically distinct region of the lung called a bronchopulmonary segment. These segments are functionally and surgically independent, making the segmental bronchi important for both respiratory function and clinical intervention.

2. Location

Tertiary bronchi are found:

• Distal to the secondary bronchi within each lobe of the lung

• Proximal to the bronchioles, forming the final cartilaginous branches of the bronchial tree

Each lung lobe contains multiple bronchopulmonary segments, each ventilated by one segmental bronchus:

• Right lung: 10 segments (3 in superior lobe, 2 in middle, 5 in inferior)

• Left lung: 8–10 segments (some segments may fuse)

3. Structure

Segmental bronchi share structural features typical of conducting airways but with reduced caliber:

• Epithelium: Lined with pseudostratified ciliated columnar epithelium with goblet cells

• Cartilage: Supported by irregular cartilage plates (not rings)

• Submucosa: Contains smooth muscle, connective tissue, and mucous glands

• Bronchial artery supply: Receives oxygenated blood from systemic bronchial arteries

Each segmental bronchus travels with a segmental artery and is separated from adjacent segments by connective tissue septa, making segments discrete functional units.

4. Function

Tertiary bronchi serve critical roles in:

• Air conduction: Direct airflow into specific bronchopulmonary segments

• Localized ventilation: Help isolate airflow to discrete anatomical regions

• Clearance and filtration: Their ciliated epithelium assists in removing debris and pathogens

5. Physiological Role(s)

In respiratory physiology, segmental bronchi support:

• Ventilation-perfusion matching: Fine-tune air distribution for efficient gas exchange

• Segmental autonomy: Each segment functions semi-independently, which helps contain infections or tumors within specific areas

• Mucociliary clearance: Propels mucus and contaminants proximally toward larger airways

6. Clinical Significance

Bronchopulmonary Segmentectomy

Due to their anatomical separation, individual segments can be surgically removed without compromising adjacent segments. This is useful for:

• Localized tumors

• Bronchiectasis

• Localized infections or abscesses

Segmental Pneumonia

Bacterial pneumonia may localize to a single bronchopulmonary segment, appearing as a sharply defined opacity on imaging. Treatment involves antibiotics, and in some cases, drainage or resection if chronic.

Segmental Obstruction

Blockage of a tertiary bronchus (by tumor, foreign body, or inflammation) can result in:

• Atelectasis (collapse) of the corresponding segment

• Post-obstructive pneumonia

• Reduced ventilation in that area

Bronchoscopy Guidance

Segmental bronchi are visualized and accessed during bronchoscopy for:

• Biopsies

• Lavage

• Targeted drug delivery

Accurate knowledge of bronchial anatomy is critical during these procedures.

Tuberculosis (TB)

TB often localizes in the upper lobes, particularly affecting specific segments like the apical-posterior segment of the upper lobe. Segmental knowledge is important in imaging interpretation and surgical planning.

Segmental Bronchiectasis

Chronic inflammation or infection may lead to segmental bronchial dilation and destruction (bronchiectasis), often requiring segmentectomy if localized and refractory to medical treatment.