Lungs - Pleura

PLEURA

General Overview

• Pleura: Serous membrane similar to peritoneum, lined by mesothelium.

• Function: Secretes serous fluid, acting as a lubricant.

• Structure: Contains two pleural sacs on either side of the mediastinum.

• Layers:

  • Parietal Pleura: Outer layer of the pleural sac.

  • Visceral (Pulmonary) Pleura: Inner layer investing the lung surfaces.

• Pleural Cavity: Potential space enclosed between the two layers.

Inner Visceral Layer

• Adherence: Closely invests all lung surfaces, except at hilum and along the pulmonary ligament.

• Extension: Penetrates into lung fissures, firmly adhering to lung surface.

Outer Parietal Layer

• Thickness: Thicker than visceral pleura; lines thoracic cavity and mediastinum.

• Divisions: Classified based on regions it covers:

  • Costal Pleura: Lines thoracic wall, separated by endothoracic fascia.

  • Diaphragmatic Pleura: Covers diaphragm.

  • Mediastinal Pleura: Lines mediastinum, continues at hilum.

  • Cervical Pleura: Dome shape, covers apex of lung, extends into the neck.

Pulmonary Ligament

• Definition: A fold extending down from the root of the lung.

• Location: Between lung and mediastinum, filled with loose areolar tissue and lymphatics.

• Functions:

  • Provides expansion space for inferior pulmonary vein during high venous return (e.g. exercise).

  • Allows descent of lung root with diaphragm during inhalation.

Surface Marking of the Pleura

Cervical Pleura

• Identification: Curved line drawn from sternoclavicular joint to clavicle's medial third.

• Position of Dome: 1 inch above the medial third of the clavicle.

Anterior (Costomediastinal) Line Reflection

• Right Side: Extends from right sternoclavicular joint to sternal angle, then vertically to xiphisternal joint.

• Left Side: Similar path, but stops at 4th costal cartilage and arches outwards to the lateral margin of the sternum.

Inferior (Costomediastinal) Line Reflection

• Right Side: Starts at xiphisternal joint, crosses ribs (8th, 10th) at specified locations.

• Left Side: Begins at 6th costal cartilage, follows similar path to right side.

Posterior (Costovertebral) Line Reflection

• Path: Ascends from the inferior reflection line to C7 vertebra side.

• Comparison of Lung and Pleura Margins:

  • Lung crosses at 6th, 8th, 10th ribs respectively.

  • Pleura crosses at 8th, 10th, 12th ribs respectively.

Pleural Recesses

• Definition: Areas in pleural cavity not occupied by lungs during quiet respiration.

Costomediastinal Recess

• Location: Anteriorly behind sternum, between costal and mediastinal pleura.

• Characteristics: Prominent in cardiac notch; left recess wider due to cardiac anatomies.

• Clinical Confirmation: Change in percussion sound indicates lung tissue present.

Costo-diaphragmatic Recess

• Location: Between costal and diaphragmatic pleurae.

• Relation to Anatomy: Right related to liver and right kidney; left to spleen and stomach.

• Significance: First spot filled by pleural effusions.

Nerve Supply, Blood Supply, and Lymphatics of the Pleura

Parietal Pleura

• Development: From somatopleuric layer of lateral plate mesoderm.

• Nerve Supply: Intercostal and phrenic nerves; pain sensitive.

• Arterial Supply: Branches from intercostal arteries, internal thoracic and musculophrenic arteries.

• Venous Drainage: Azygos and internal thoracic veins; lymphatics into intercostal, internal mammary nodes.

Pulmonary Pleura

• Development: From splanchnopleuric layer.

• Nerve Supply: Autonomic (T2-T5); pain insensitive.

• Blood Supply: Bronchial vessels; lymphatics to bronchopulmonary nodes.

Functional Importance of the Pleural Cavity

• Nature of Space: Potential space with mesothelial cells lining.

• Fluid Secretion: Serous fluid for lung movement.

• Pressure Maintenance: Negative pressure essential to keep lungs expanded against thoracic wall.

• Pneumothorax Effect: Positive pressure leads to lung collapse.