Pleura

Thorax Anatomy

Pleurae

General overview, layers, embryological aspects, pulmonary and parietal pleura, pulmonary ligament, recesses, nerve supply, blood supply, lymphatic drainage and clinical anatomy.

1

General Overview

  • Like the peritoneum, the pleura is a serous membrane which is lined by mesothelium (flattened epithelium).
  • There are two pleural sacs, one on either side of the mediastinum.
2

Layers of the Pleura

Each pleural sac is invaginated from its medial side by the lung, so that it has two layers:

Parietal Pleura

Outer layer

Visceral or Pulmonary Pleura

Inner layer

  • The two layers are continuous with each other around the hilum of the lung.
  • Enclose between them a potential space called the pleural cavity.
3

Embryological Aspects of Pleural Cavities

  • During embryonic life, foetus has two pleural sacs (initially called pericardioperitoneal canals).
  • Each developing lung bud invaginates one pleural sac and gets covered by two layers of pleural sac.
  • Later, lung bud expands to form the lung and starts occupying the pleural sac.
  • Layer of the pleural sac covering the lung forms visceral pleura.
  • Outer layer forms the parietal pleura.
  • A thin persistent space between two layers of pleura forms the pleural cavity.
4

Pulmonary / Visceral Pleura

  • The serous layer of pulmonary pleura covers the surfaces and fissures of the lung.
  • Exceptions: Does not cover at the hilum and along the attachment of the pulmonary ligament where it is continuous with the parietal pleura.
  • It also extends into the depths of the fissures of the lungs.
  • It is firmly adherent to the lung and cannot be separated from it.
5

Parietal Pleura

  • The parietal pleura is thicker than the pulmonary pleura.
  • It is subdivided into the following four parts:
Costal
Diaphragmatic
Mediastinal
Cervical

1. Costal Pleura

  • Lines the thoracic wall which comprises ribs and intercostal spaces.
  • Loosely attached to thoracic wall by a layer of areolar tissue called the endothoracic fascia.

2. Mediastinal Pleura

  • Lines the corresponding surface of the mediastinum.
  • Reflected over the root of the lung and becomes continuous with the pulmonary pleura around the hilum.

3. Cervical Pleura

  • Extends into the neck, nearly 5 cm above the first costal cartilage and 2.5 cm above the medial 1/3rd of the clavicle.
  • Covers the apex of the lung.
  • Covered by the suprapleural membrane.

Relations of Cervical Pleura

Anterior
Subclavian artery, inner border of the first rib, scalenus anterior muscle
Posterior
Neck of the first rib
Lateral
Inner border of the first rib, scalenus medius muscle
Medial
Major vessels of the neck
Superior
Suprapleural membrane, supraclavicular part of brachial plexus
Inferior
Apex of lung

4. Diaphragmatic Pleura

  • Lines the superior aspect of diaphragm.
  • Covers the base of the lung.
  • Gets continuous with mediastinal pleura medially and costal pleura laterally.
6

Pulmonary Ligament

Definition

The parietal pleura surrounding the root of the lung extends downwards beyond the root as a fold called the pulmonary ligament.

Contents

  1. Space of the pulmonary ligament is filled with loose areolar tissue
  2. Few lymphatics
  3. Sometimes accessory bronchial artery

Functions

  1. Potential space: Provides a potential (dead) space for the expansion of pulmonary veins.
  2. Permit descent of root of lungs: During inspiration, provides space for the descent of root of lungs (descent of diaphragm pulls the lung downward).
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Recesses of Pleura

There are two recesses of parietal pleura, which act as “reserve spaces” for the lung to expand during deep inspiration:

1. Costomediastinal Recress

  • Lies anteriorly, behind the sternum and costal cartilages, between the costal and mediastinal pleurae.
  • Particularly in relation to the cardiac notch of the left lung.
  • Filled up by the anterior margin of the lungs even during quiet breathing.
  • Only obvious in the region of the cardiac notch of the lung.

2. Costodiaphragmatic / Costovertebral Recess

  • Lies inferiorly between the costal and diaphragmatic pleurae.
  • Vertically, it measures about 5 cm.
  • Extends from the eighth to tenth ribs along the midaxillary line.
  • During inspiration, the lungs expand into these recesses.
  • Obvious only in expiration and not in deep inspiration.
8

Nerve Supply of the Pleura

1. Parietal Pleura

  • Develops from the somatopleuric layer of the lateral plate mesoderm.
  • Supplied by somatic nerves (intercostal and phrenic nerves).

Pain sensitive

  • Costal and peripheral parts of diaphragmatic pleurae: Supplied by intercostal nerves.
  • Mediastinal pleura and central part of diaphragmatic pleurae: Supplied by phrenic nerves (C4).

2. Pulmonary / Visceral Pleura

  • Develops from the splanchnopleuric layer of the lateral plate mesoderm.
  • Supplied by autonomic nerves:
  • Sympathetic nerves: Derived from 2nd to 5th sympathetic ganglia.
  • Parasympathetic nerves: Drawn from the vagus nerve.
  • Nerves accompany the bronchial vessels.
Not sensitive to pain.

Functions

  • Sympathetic system dilates the bronchi.
  • Parasympathetic system narrows the bronchial tree and is secretory to the glands.
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Blood Supply and Lymphatic Drainage of Pleura

1. Parietal Pleura

Part and parcel of the thoracic wall; blood supply and lymphatic drainage are the same as that of the body wall.

Arterial Supply

Intercostal, internal thoracic, and musculophrenic arteries.

Venous Drainage

Veins drain mostly into the azygos and internal thoracic veins.

Lymphatic Drainage

Intercostal, internal mammary, posterior mediastinal, and diaphragmatic nodes.

2. Pulmonary Pleura

Like the lung, supplied by the bronchial arteries.

Venous Drainage

Drains into bronchial veins.

Lymphatic Drainage

Drained by the bronchopulmonary lymph nodes.

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Clinical Anatomy

Paracentesis Thoracis

  • Aspiration of any fluid from the pleural cavity.
  • Usually done in the 8th intercostal space in the midaxillary line.
  • The needle is passed through the lower part of the space to avoid injury to the principal neurovascular bundle, i.e., vein, artery, and nerve (VAN).

Pleurisy

  • Inflammation of the pleura.
  • May be dry, but often accompanied by collection of fluid in the pleural cavity (pleural effusion).
  • Dry pleurisy is more painful because during inspiration both layers come in contact and there is friction.

Pneumothorax

Presence of air in the pleural cavity.

Tension Pneumothorax

  • A surgical emergency.
  • Occurs when air can enter into the pleural space but cannot escape due to valvular air passage (one-way entry of air).
  • Causes collapse of lungs, impairment of respiration, hyperexpansion of chest, and deviation of trachea to the opposite side.
  • Requires emergency thoracostomy (insertion of needle in the 2nd intercostal space in the midclavicular line).

Haemothorax

Presence of blood in the pleural cavity.

Hydropneumothorax

Presence of both fluid and air in the pleural cavity.

Pleurae — Study Notes