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1. Shape and Structure

  • Asymmetrical shape: The left lung is narrower but longer than the right lung.

  • Weight: It weighs less than the right lung, contributing to the asymmetry in the thorax.

  • Lobes: The left lung consists of two lobes:

    1. Superior lobe

    2. Inferior lobe

Lobes and Fissure

  • Oblique fissure: Separates the superior and inferior lobes, running diagonally across the lung.

2. Features:

  • Cardiac Notch: A concave indentation on the anterior surface of the superior lobe to accommodate the heart.

Lingula

  • A small tongue-like projection located on the inferior part of the superior lobe, below the cardiac notch. It is a remnant of what could be considered a middle lobe (present in the right lung).

3. Surfaces

  • Costal surface: Faces the ribs; smooth and convex to match the contour of the rib cage.

  • Mediastinal surface: Faces the heart and mediastinum, where the cardiac notch is present.

  • Diaphragmatic surface: Rests on the diaphragm; slightly concave.

4. Hilum and Root of the Lung

The hilum is the gateway where structures enter and exit the lung. It contains:

  • Primary bronchus: Carries air to and from the trachea.

  • Pulmonary arteries: Deliver deoxygenated blood to the lungs.

  • Pulmonary veins: Return oxygenated blood to the heart.

  • Lymphatic vessels and nerves are also present.

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5. Vasculature and Bronchi

  • Left pulmonary artery: Branches off the pulmonary trunk and enters the lung at the hilum.

  • Pulmonary veins: Two veins (superior and inferior) exit the lung, returning oxygenated blood to the left atrium.

  • Left bronchus: The primary bronchus branches into segmental bronchi (one per bronchopulmonary segment).

6. Bronchopulmonary Segments

The left lung is divided into 8-9 segments:

  • Superior lobe:

    • Apical-posterior segment

    • Anterior segment

  • Inferior lobe:

    • Superior segment

    • Anteromedial basal segment

    • Lateral basal segment

    • Posterior basal segment

These segments are functionally independent and can be removed individually if necessary (e.g., during surgery).

7. Pleura

The lung is surrounded by a double-layered membrane called the pleura:

  • Visceral pleura: Adheres directly to the lung’s surface.

  • Parietal pleura: Lines the chest wall, diaphragm, and mediastinum.

  • Pleural cavity: A thin space between the two layers, filled with pleural fluid to reduce friction during breathing.

Left Lung

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