Inferior lobe of left lung

At a glance

English

Inferior lobe of left lung

Latin (TA2)

Lobus inferior pulmonis sinistri

System

Respiratory

Region

Thorax

Side

Single, on the midline

About the inferior lobe of left lung

The inferior lobe of the left lung occupies the back and base of the left side of the chest. It is cut off from the upper lobe by the oblique fissure. This begins at the back of the lung near the level of the third or fourth thoracic spine, sweeps downwards and forwards round the side of the chest and reaches the lower border near the sixth costal cartilage. All the lung behind and below this line is lower lobe. Seen from behind it makes up most of the left lung; seen from the front it shows only as a strip at the bottom.

Its base is concave and fits over the left dome of the diaphragm, under which lie the spleen, the stomach and the left lobe of the liver. Its medial surface lies behind the heart and against the descending aorta, which grooves it, and the oesophagus near its lower part. Its lower edge dips into the costodiaphragmatic recess of the pleura during deep breathing in.

Air reaches it through the left inferior lobar bronchus. A superior segmental bronchus leaves its back first, and the trunk then gives the basal bronchi. On the left the anterior and medial basal bronchi usually start from a common stem, so the segments are counted as superior, anteromedial basal, lateral basal and posterior basal, though five are named as on the right. The left pulmonary artery winds behind the bronchus to supply the lobe, and the left inferior pulmonary vein drains it.

Because the heart lies in front of it, disease in the left lower lobe can be hard to see on a frontal X-ray; a collapse shows as a triangular density behind the heart and loss of the outline of the descending aorta or left diaphragm. Like its right counterpart it receives aspirated material, though less often, since the left main bronchus is angled more sharply.

Function and supply

Function

Carries out gas exchange in the back and base of the left lung, where blood flow is greatest in the upright body.

Nerve supply

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

Blood supply

Lower-lobe branches of the left pulmonary artery for gas exchange and left bronchial arteries for the tissue; drained by the left inferior pulmonary vein.