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According to the course of the conduits, the left lung is divided into 9 segments. In contrast to the right side, the 7th segment is absent due to the position of the heart. The left upper lobe consists of 5 bronchopulmonary segments, as it includes the equivalent to the right middle lobe, the lingula (segments 4 and 5).
- The segments S1 to S3
- Are subdivided analogously to the right upper lobe into an apical segment (S1), a posterior segment (S2), and an anterior segment (S3).
- The segments S4 and S5 form the so-called lingula, corresponding to the middle lobe on the right side.
Bronchus B1-3:
The left main bronchus, at approximately 5 cm in length, is significantly longer than the right main bronchus. The left upper lobe bronchus runs laterocranially and divides after 10-12 mm into the apicoposterior segmental bronchus (B1 and B2) and the anterior segmental bronchus (B3). The lingula bronchus of segments 4 and 5 runs ventrocaudally and divides after about 10 mm into the segmental bronchi B4 and B5.
Arteries A1-3:
The left pulmonary artery runs ventrally to the left main bronchus in a posterolateral direction to the lung hilum. It continues over the left upper lobe bronchus dorsally to extend into the interlobar fissure. It initially gives off the segmental arteries A1 and A2 (either as a common trunk or separately). In the interlobar portion, further branches are initially given to the anterior segment (A3) and subsequently to the lingula (often a common trunk A4 and A5).
Vein V1-3:
The left upper lobe drains its blood over the front of the hilum into the superior pulmonary vein. The segments 4 and 5 (lingula) drain the blood analogously to the right middle lobe, usually via a common vein also into the left superior pulmonary vein, rarely into the inferior pulmonary vein.