Middle lobe of right lung

At a glance

English

Middle lobe of right lung

Latin (TA2)

Lobus medius pulmonis dextri

System

Respiratory

Region

Thorax

Side

Single, on the midline

About the middle lobe of right lung

The middle lobe exists only on the right. It is a wedge-shaped piece of lung bounded above by the horizontal fissure, which separates it from the upper lobe, and below and behind by the lower part of the oblique fissure, which separates it from the lower lobe. Its broad outer surface faces forwards and to the side against the lower front ribs, while its narrow inner end points back towards the hilum. On the left, the lingula of the upper lobe occupies a similar position and plays the same part.

The horizontal fissure leaves the oblique fissure at about the midaxillary line and runs forwards roughly along the fourth rib to the front of the lung at the level of the fourth costal cartilage. The oblique fissure runs downwards and forwards to meet the lower border near the sixth costal cartilage. Between these lines lies the lobe. Its medial surface rests against the right side of the heart within the pericardium, and its lower surface sits on the front part of the right dome of the diaphragm.

Air reaches it through the middle lobar bronchus, which arises from the front of the intermediate bronchus. This divides into lateral and medial segmental bronchi, so the lobe has two bronchopulmonary segments. Its arterial supply comes from a middle-lobe branch of the right pulmonary artery, and its veins join the right superior pulmonary vein.

The lobe has a reputation for trouble. Its bronchus is long and narrow and surrounded by lymph nodes, and its fissures often cut it off from collateral air flow, so it collapses or becomes infected repeatedly in the middle lobe syndrome. Because it touches the heart, consolidation or collapse here blurs the right heart border on a frontal chest X-ray. The horizontal fissure is often incomplete, and the lobe may then be partly fused with the upper lobe.

Function and supply

Function

Exchanges gases between inspired air and the blood in the lower front part of the right lung.

Nerve supply

Pulmonary plexus (vagal and sympathetic fibres), with visceral sensory fibres for stretch and cough reflexes.

Blood supply

Middle-lobe branches of the right pulmonary artery for gas exchange and the right bronchial artery for the tissue; drained by the right superior pulmonary vein.