The Pleura

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THE  PLEURA

  • Pleura is a closed serous sac enclosing a pleural cavity filled with pleural fluid.
  • It is divided into right & left pleural sacs by the invagination of lungs.
  • Each pleural sac consists of..
    • Inner Visceral / Pulmonary Pleura  &
    • Outer Parietal Pleura


VISCERAL / PULMONARY  PLEURA :-

  • It intimately invests the entire lung except at the hilum & pulmonary ligament where it is continuous with the parietal layer of pleura.

PARIETAL  PLEURA :-

  • It is subdivided into 4 parts according to the structures it lines..

Costal Pleura

Mediastinal Pleura

Diaphragmatic Pleura

Cervical Pleura

COSTAL  PLEURA :-

  • It lines the inner surfaces of sternum, ribs, costal cartilages, intercostal spaces & the sides of vertebral bodies.
  • It is separated from the above structures by endothoracic fascia.

Reflexions -

In front -

  • It is continuous with mediastinal pleura along the costo-mediastinal line of reflexion.
  • On the right side the line extends-

downwards & medially from sterno-clavicular joint to sternal angle

descends vertically from sternal angle to xiphisternal joint

turns laterally across the costo-xiphoid angle 

follows the 7th costal cartilage

  • On the left side the line extends-

downwards & medially from sterno-clavicular joint to sternal angle


descends vertically from sternal angle to 4th costal cartilage

deviates laterally till 6th costal cartilage (because of cardiac notch of left lung)

follows the 7th rib

Behind -

  • It is continuous with mediastinal pleura along the costo-vertebral line of reflexion.
  • The line extends vertically from 2.5cm lateral to 7th cervical spine to 2.5cm lateral to 12th thoracic spine.

Above -

  • It is continuous with cervical pleura along the inner border of 1st rib.

Below -

  • It is continuous with diaphragmatic pleura along the costo-diaphragmatic line of reflexion.
  • On the right side the line extends-

Xiphisternal joint anteriorly

8th costal cartilage in the mid-clavicular line

10th rib in the mid-axillary line

2.5cm lateral to 12th thoracic spine posteriorly

  • On the left side the line extends-

6th costo-sternal joint anteriorly

8th costal cartilage in the mid-clavicular line

10th rib in the mid-axillary line

2.5cm lateral to 12th thoracic spine posteriorly

MEDIASTINAL  PLEURA :-

  • It is subdivided into 3 parts.. above the lung root, at the lung root & below the lung root.

Above the Lung Root -

  • It forms an antero-posterior sheet from sternum to vertebral column.
  • On the right side it is related to-
    • Right brachio-cephalic vein, superior vena cava, arch of azygos vein, brachio-cephalic trunk, right phrenic & vagus nerves, esophagus & trachea.
  • On the left side it is related to-
    • Arch of aorta, left common carotid & subclavian arteries, left brachio-cephalic & superior intercostal veins, left phrenic, vagus & recurrent laryngeal nerves, esophagus & thoracic duct.

At the Lung Root -

  • It forms a tubular lung root to enclose the structures which enter or leave the lung.
  • Lung root extends from mediastinum to hilum of the lung.
  • At the hilum it continues with the pulmonary pleura.
  • At the mediastinum its layers diverge anteriorly & posteriorly.
  • Anteriorly-
    • Covers the fibrous pericardium as pericardial pleura & continuous with costal pleura along the costo-mediastinal line of reflexion.
  • Posteriorly-
    • Continuous with costal pleura along the costo-vertebral line of reflexion.
Arrangement of structures within the lung root-
  • From anterior to posterior- (VAB) 
    • Superior pulmonary vein, pulmonary artery, bronchus.
  • From above downwards- 
    • On the right side- (BABI) Eparterial bronchus, pulmonary artery, hyparterial bronchus, inferior pulmonary vein.
    • On the left side- (ABI) Pulmonary artery, principal bronchus, inferior pulmonary vein.

Below the Lung Root -

  • It forms a bilaminar fold known as pulmonary ligament.

Pulmonary ligament-

  • It is a collapsed portion of lung root, acts as a dead space.
  • It lies below the hilum & extends from lung to the esophagus.
  • Above- the two layers of ligament are continuous with lung root.
  • Below- they are fused to form a free margin.
  • Contents- loose areolar tissue, lymphatics, occasionally accessory bronchial artery.
  • Function- allows the free expansion of inferior pulmonary vein during venous return.

DIAPHRAGMATIC  PLEURA :-

  • It covers the thoracic surface of diaphragm.
  • Laterally-
    • It is continuous with costal pleura along the costo-diaphragmatic line of reflexion.
  • Medially-
    • It is continuous with mediastinal pleura along the attachment of fibrous pericardium to central tendon of diaphragm.

CERVICAL  PLEURA :-

  • It extends from inner border of the 1st rib to apex of the lung.
  • Laterally- It is continuous with costal pleura.
  • Medially- It is continuous with mediastinal pleura.
  • Summit- Lies 3-4cm above the 1st costal cartilage & 2.5cm above the sternal end of clavicle.

Supra-pleural Membrane (Sibson’s fascia) -

  • It is a dome shaped musculo-fascial expansion, covers the summit of cervical pleura.
  • It is derived from scalenus minimus muscle & endo-thoracic fascia.
  • Laterally, it is attached to the tip of transverse process of 7th cervical vertebra & inner border of 1st rib.
  • Medially, it is continuous with pretracheal fascia of the neck.

 


PLEURAL  RECESSES :-

  • They are the recesses of parietal pleura.
  • Act as reserve spaces for the lung to expand during deep inspiration.
    • Costo-diaphragmatic Recess
    • Costo-mediastinal Recess


Costo-diaphragmatic Recess –

  • It is a potential space between the lower limits of pleura & its corresponding lung.
  • It is widest in the mid-axillary line between 8th – 10th ribs (5cm).
  • It is the most dependent part of the pleural sac.
  • It allows expansion of the lung in full inspiration.
  • On the right side it is related to-
    • Right lobe & caudate lobe of the liver, posterior surface of right kidney.
  • On the left side it is related to-
    • Fundus of stomach, spleen, posterior surface of left kidney.

Costo-mediastinal Recess –

  • It lies between the costal & mediastinal pleura.
  • Filled with anterior margin of the lung.
  • Prominent in the region of cardiac notch of left lung.

 

NERVE  SUPPLY  OF  PLEURA :-

Pulmonary Pleura is innervated by autonomic nerves.

  • Sympathetic fibres from T2-T5.
  • Parasympathetic fibres from vagus nerve.

Parietal Pleura is innervated by spinal nerves.

  • Costal & peripheral part of diaphragmatic pleura by intercostal nerves.
  •  Cervical, mediastinal & medial part of diaphragmatic pleura are supplied by phrenic nerves.

 

DEVELOPMENT  OF  PLEURA :-

Pulmonary Pleura is developed from splanchnopleuric layer of lateral plate mesoderm.

Parietal Pleura is developed from somatopleuric layer of lateral plate mesoderm.

 

APPLIED  ASPECTS :-

Pleurisy / Pleuritis -

  • It is the inflammation of pleura. It may be..
    • Dry Pleurisy
    • Pleural Effusion

Dry Pleurisy-

  • Both the layers of pleura become rough.
  • Friction rub may be heard on auscultation.
  • Symptoms- chest pain, cough, rise of temperature.
  • The pain may be referred to the anterior abdominal wall or root of the neck & shoulder, depending on the part of parietal pleura involved.

Pleural Effusion-

  • Accumulation of significant amount of fluid in the pleural cavity.
  • Progressive accumulation of fluid allows retraction of the lung towards its hilum, displaces the heart & mediastinum to the opposite side.
  • Cause- inflammation, chest trauma, congestive heart failure.
  • Types-
    • Hydrothorax- accumulation of watery secretion
    • Pyothorax- accumulation of pus
    • Haemothorax- accumulation of blood
    • Chylothorax- accumulation of chyle (lymph)

Pleural Tap (Paracentesis Thoracis) -

  • Surgical aspiration of pleural fluid.
  • Performed posterior to the mid-axillary line below the fluid level (or 8th Intercostal pace) with the patient in sitting position.

Pneumothorax -

  • Entry of air into the pleural cavity.
  • Cause- penetrating thoracic wound, rupture of pulmonary bulla, fractured ribs, needle punctures.
  • Results in- collapse of the lung, mediastinal contents displaced to the opposite side.
  • Types- Open pneumothorax & Closed pneumothorax

Open Pneumothorax-

  • Pleural cavity is exposed to the atmosphere due to rupture of parietal pleura.
  • Mediastinal contents shift-
    • to normal side during inspiration due to sucking air in.
    • to injured side during expiration due to blowing air out.

Closed Pneumothorax-

  • A valvular opening in the visceral pleura permits air entry into the pleural cavity during inspiration but prevents air exit during expiration.
  • Leads to rapid increase in air volume & lung collapse, producing Tension Pneumothorax.
  • A chest tube is inserted in to the pleural cavity through anterior part of 2nd intercostal space to release the air.

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