Tertiary Bronchi

Tertiary bronchi, also known as segmental bronchi, are the third-order branches of the bronchial tree. They arise from the secondary (lobar) bronchi and each supplies a single bronchopulmonary segment - an anatomically and functionally independent unit of the lung. These bronchi represent the last portion of the conducting bronchial tree supported by cartilage, after which they transition into smaller bronchi and bronchioles.

Location

Tertiary bronchi are located within the lung parenchyma, distal to the lobar bronchi. They branch deeper into the lungs and form the anatomical foundation for bronchopulmonary segments. These bronchi are completely intrapulmonary and closely associated with pulmonary artery branches, both of which supply their respective segments.

Branching Hierarchy

The bronchial tree branches as follows:

1. Trachea

2. Primary (main) bronchi

3. Secondary (lobar) bronchi

4. Tertiary (segmental) bronchi

5. Smaller bronchi → bronchioles → terminal and respiratory bronchioles

Each tertiary bronchus is named based on the bronchopulmonary segment it supplies.

Bronchopulmonary Segments

Each tertiary bronchus supplies a bronchopulmonary segment - an independent, pyramid-shaped unit of the lung with its own bronchial and arterial supply. These segments are separated by connective tissue septa, allowing for individual surgical resection.

Right Lung (10 segments)

Superior Lobe

1. Apical

2. Posterior

3. Anterior

Middle Lobe

1. Lateral

2. Medial

Inferior Lobe

1. Superior

2. Medial basal

3. Anterior basal

4. Lateral basal

5. Posterior basal

Left Lung (8–10 segments)

Superior Lobe

1. Apicoposterior (may be combined)

2. Anterior

3. Superior lingular

4. Inferior lingular

Inferior Lobe

1. Superior

2. Anteromedial basal (anterior and medial may fuse)

3. Lateral basal

4. Posterior basal

Structure

Tertiary bronchi have smaller diameters than lobar bronchi but still retain cartilage and mucosal structures:

• Epithelium: Ciliated pseudostratified columnar epithelium

• Cartilage: Irregular plates of hyaline cartilage (not rings)

• Muscular layer: Circular smooth muscle deep to the mucosa

• Submucosa: Contains mucous glands

These bronchi are the last airway branches to contain cartilage in their walls. Beyond the tertiary level, cartilage is replaced entirely by smooth muscle and elastic tissue in bronchioles.

Function

• Conduct air into individual bronchopulmonary segments

• Support mucociliary clearance via ciliated epithelium

• Allow segmental isolation of lung tissue for surgical or diagnostic purposes

Segmental Autonomy

Because each tertiary bronchus serves an independent segment, bronchopulmonary segments:

• Have their own air and arterial supply

• Are drained intersegmentally by pulmonary veins

• Can be removed individually via segmentectomy

Blood Supply

• Arterial: Branches of pulmonary arteries follow the tertiary bronchi into each segment

• Bronchial arteries: Supply nutrition to bronchial walls and surrounding structures

• Venous drainage: Segmental veins drain into intersegmental pulmonary veins

Innervation

• Parasympathetic (vagus nerve): Bronchoconstriction, increased mucus secretion

• Sympathetic (thoracic spinal nerves): Bronchodilation, decreased secretion

• Visceral afferents: Sense stretch and irritants

Lymphatic Drainage

• Drains to pulmonary → bronchopulmonary (hilar) → tracheobronchial lymph nodes

• Segmental nodes may exist within bronchopulmonary segments in some individuals

Clinical Relevance

• Segmentectomy: Tertiary bronchi allow surgical removal of diseased segments without affecting neighboring lung regions

• Localized infection: Infections like tuberculosis or pneumonia may remain confined to a single bronchopulmonary segment

• Bronchoscopic access: Advanced bronchoscopes can visualize or access tertiary bronchi for biopsy, lavage, or stent placement