Left inferior lobar bronchus

At a glance

English

Left inferior lobar bronchus

Latin (TA2)

Bronchus lobaris inferior sinister

System

Respiratory

Region

Thorax

Side

Single, on the midline

About the left inferior lobar bronchus

The left inferior lobar bronchus is the continuation of the left main bronchus after the superior lobar bronchus has left it. It passes downwards and backwards into the lower lobe, which reaches from the oblique fissure to the base of the lung and extends high up at the back, roughly to the level of the fourth thoracic vertebra.

Shortly after its start it gives off, from its back wall, the superior segmental bronchus, which turns backwards to the top of the lower lobe. The trunk then continues as a basal stem and divides into the basal segmental bronchi. On the left the anterior and medial basal branches usually arise together as a common anteromedial bronchus, so the lower lobe has four rather than five main segmental airways: superior, anteromedial basal, lateral basal and posterior basal.

The wall contains irregular cartilage plates, a spiral smooth muscle coat and a ciliated mucosa with glands. The left pulmonary artery winds round behind the bronchus, lying lateral and posterior to it as both descend into the lobe, while the inferior pulmonary vein lies below and in front.

Because the lower lobes are the most dependent parts of the lungs in an upright person, secretions and inhaled material tend to collect in them, and the superior segment is a common site of aspiration when lying on the back. The left lower lobe sits behind the heart, so collapse or consolidation here may be hidden on a frontal chest X-ray and is looked for as a triangular density behind the cardiac shadow.

Function and supply

Begins at

The left main bronchus within the hilum, below the origin of the superior lobar bronchus.

Ends at

Divides into the superior segmental bronchus and the basal segmental bronchi (anteromedial, lateral and posterior basal).

Function

Conducts air to and from the lower lobe of the left lung.

Nerve supply

Pulmonary plexus (vagal and sympathetic fibres).

Blood supply

Left bronchial arteries from the descending thoracic aorta.