Lobes of the Left Lung

The left lung consists of two lobes: the superior (upper) lobe and the inferior (lower) lobe. These lobes are separated by a single oblique fissure. Despite having fewer lobes than the right lung, the left lung has a comparable number of bronchopulmonary segments and serves an equivalent role in respiration. The left lung also features a unique anatomical indentation called the cardiac notch, accommodating the heart.

Location

The left lung occupies the left hemithorax, lateral to the mediastinum and superior to the diaphragm. It is slightly smaller and narrower than the right lung due to displacement by the heart. The apex extends above the clavicle, while the base rests on the diaphragm.

Surfaces

Like the right lung, the left lung has three surfaces:

• Costal surface: Smooth and convex; lies adjacent to the inner surface of the ribs
• Mediastinal surface: Concave; faces the mediastinum and heart; includes the hilum and cardiac notch
• Diaphragmatic surface: Inferior surface resting on the diaphragm; slightly concave

Fissure of the Left Lung

Oblique Fissure

• Separates the superior and inferior lobes
• Extends from the T2 vertebra posteriorly down to the 6th costochondral junction anteriorly

Unlike the right lung, the left lung lacks a horizontal fissure and middle lobe.

Lobes of the Left Lung

1. Superior (Upper) Lobe

• Occupies the anterior and superior portion of the lung
• Contains the lingula, a tongue-like projection that corresponds to the middle lobe of the right lung
• Receives air via the left superior lobar bronchus
• Contains four or five bronchopulmonary segments depending on anatomical variation

2. Inferior (Lower) Lobe

• Occupies the posteroinferior portion of the lung
• Larger than the superior lobe
• Receives air via the left inferior lobar bronchus
• Contains four or five bronchopulmonary segments

Bronchopulmonary Segments of the Left Lung

Each lobe is divided into bronchopulmonary segments—functionally and anatomically discrete regions, each supplied by a segmental (tertiary) bronchus:

Superior Lobe

1. Apicoposterior segment (often considered a fusion of apical and posterior)
2. Anterior segment
3. Superior lingular segment
4. Inferior lingular segment

Inferior Lobe

1. Superior segment
2. Anteromedial basal segment (anterior and medial often fused)
3. Lateral basal segment
4. Posterior basal segment

In total, the left lung typically has 8–10 segments, depending on whether the apical/posterior and anterior/medial segments are counted separately.

Lingula

The lingula is a thin, tongue-shaped projection of the left superior lobe that wraps around the left side of the heart. It corresponds topographically to the right lung’s middle lobe and consists of:

• Superior lingular segment
• Inferior lingular segment

Although not a distinct lobe, the lingula functions similarly and plays a critical role in gas exchange.

Vascular Supply

Arterial

• Pulmonary arteries: Carry deoxygenated blood from the right ventricle to each lung segment via segmental branches
• Bronchial arteries: Supply oxygenated blood to the lung tissue itself

Venous

• Pulmonary veins: Drain oxygenated blood into the left atrium
• Veins course between segments (intersegmental)

Innervation

• Parasympathetic: From the vagus nerve (CN X); promotes bronchoconstriction and glandular secretion
• Sympathetic: From thoracic sympathetic trunk; causes bronchodilation
• Visceral afferents: Monitor stretch, irritation, and pain (referred)

Lymphatic Drainage

• Superficial and deep lymphatic plexuses
• Drain into pulmonary → bronchopulmonary (hilar) → tracheobronchial → paratracheal nodes

Surface Anatomy

• Anterior border features the cardiac notch and lingula
• Lung extends to rib 6 at the midclavicular line, rib 8 at the midaxillary line, and T10 posteriorly
• Oblique fissure aligns with the 5th rib at the midaxillary line

Clinical Relevance

• Cardiac notch: Allows pericardiocentesis access without lung injury
• Lobectomy: Individual lobes may be surgically removed due to distinct bronchovascular supplies
• Segmentectomy: Allows for removal of specific diseased segments while preserving healthy lung