Pleura and Pleural Recesses

Learning Objective

After reading this post you will know the following about pleura  and pleural recesses:

  • Definition of  pleura and pleural cavity.
  • Characteristics of  different layers of pleura.
  •  Subdivisions of parietal pleura.
  • Sites where parietal pleura extends beyond the thoracic cage.
  • Pleural ligament and its functions.
  • Pleural recesses and their clinical significance.
  • Anatomical basis of pleural rub in pleuritis, site of  pleura tap, causes of pneumothorax and pleural effusions.
  • Nerve supply of pleura and anatomical basis of  referred pain  in inflammation of  different parts of parietal pleura.

Q. Define:

  1. Pleura
  2. Pleural cavity

 A. 1. Pleura is a serous membrane lined by  mesothelium(simple squamous epithelium)  that  is present as a closed sac  around the lungs. It comprises of two layers, outer parietal and inner  visceral layer.

2. Pleural cavity is a closed potential space between the parietal and visceral layers of  pleura. It normally contains   only a thin film of serous fluid which is secreted by the pleura. The space becomes apparent  if  there is  accumulation of air  (pneumothorax), blood (haemothorax) or pus (empyema).                                                                        

 Layers of Pleura

 Q. What are the characteristic features of

  1. Parietal pleura
  2. Visceral pleura

A. 1. Characteristic features of visceral pleura:Layers of pleura

  1. It is the inner layer of the two layers of pleura.
  2. It is tightly adherent to the outer surface of lung .
  3. It also lines the fissures of the lung.
  4. It does not cover the hilum of the lung and the area along which pulmonary ligament is attached.
  5. It develops from the splanchnopleuric layer of the mesoderm.
  6. It is innervated by the autonomic nervous system and is therefore  insensitive to pain.
  7. It is continuous with the parietal layer at the root of lung.

2. Characteristic features of parietal pleura.

  1. It is the outer layer of the two layers of the two layer.
  2. It lines the corresponding half of the thoracic wall separated from it by endothoracic fascia(areolar  tissue), covers the thoracic surface of  diaphragm  and the mediastinum.
  3. It develops from the somatopleuric layer of the mesoderm.
  4. It is innervate by the somatic nervous system and is therefore sensitive to pain.

Q. What are the various subdivisions of parietal pleura?

A. Parietal pleura is given different names  that correspond to the  structures with which it is  associated.

  1. Cervical: Dome shaped pleura extending into the neck (summit is 2.5cm above the clavicle)
  2. Costal: Lines the ribs and intercostal spaces.
  3. Diaphragmatic: Pleura covering the diaphragm
  4. Mediastinal: Pleura covering the mediastinum.

Subdivisions of Parietal Pleura

      Sites where the parietal pleura extends beyond the thoracic cage and is in danger of being injured.

  • Above the medial 1/3rd of the clavicle on both the sides
  • Beyond the right xiphicostal angle
  • Below costovertebral angle on both the sides.

Q. What is Pulmonary ligament?

A.  Pulmonary ligament : It is  the narrow fold of parietal pleura  that extend  below the root of  lung.

  Functions of pulmonary ligament are:

  • Allows  descent of structures of root of lung during inspiration.
  • Provides dead space into which pulmonary vein can expand during increased venous return ( e.g. during exercise).

Pulmonary ligament

Peural Recesses

Q. Describe pleural recesses.

A. Pleural recesses: Anterior and inferior regions of pleural cavities are normally not  occupied by the lungs. In these regions the two layers  of  parietal  pleura  are opposed  to each other resulting in presence of potenial spaces called pleural recesses .  These recesses  allow expansion of lungs during inspiration. The two recesses of the pleura are:

  • Right and laeft costomediastinal recesses
  • Right and left costodiaphragmatic recesses

Costodiaphragmatic recesss:

  • Is the largest and clinically most important recess.
  • Is present between the costal and diaphragmatic parts of parietal pleura.
  • Is C- shaped and present between the inferior margins of the lungs and the inferior margin of the pleural cavities.
  • The maximum vertical distance is 5 cm along the midaxillary line opposite to 8th-10th
  • Is the most dependent part of the pleural cavity  and therefore the fluid of pleural effusions first collect here.

Costomediastinal recess:

    • Is present anteriorly between the costal and mediatinal pleura.
    • The left costomediastinal recess is larger due to the presence of cardiac notch along the anterior border of the left lung.

pleural recesses

Q. Describe briefly the following.

  1. Pleurisy or pleuritis
  2. Pleural tap
  3. Pneumothorax
  4. Pleural effusions

A.  a. Pleurisy/Pleuritis: Pleurisy is inflammation of the  pleural membranes. The condition is  very painful especially when a person takes deep breath.  During respiratory movements, the  parietal and visceral  layers slide past  other. Normally the  pleural  fluid in the  pleural  cavities lubricates the surfaces of  these membranes.When the  pleural membranes  are inflamed , their surfaces become  rough , the  rough  surfaces rub against each other   and produce pain. Due to the friction between  the two layers of pleura  during the  respiratory movements, pleural  rub can be with the stethoscope.

b. Pleural tap: It is aspiration of pleural effusion from the pleural cavity.  It is usually done in the 9th intercostal space   in the  midaxillary line . The needle  is inserted just  above the upper border of the rib in  the lower part of the   intercostal space  to avoid  injury to the intercostal nerves and vessels. The needle should not be inserted below  the 9th  intercostal space , lest it may injure the spleen on the left  side and liver on the  right side.

pleural tap or paracentesis thoracis

c. Pneumothorax: Presence of air in the pleural cavity is known as pnemothorax.  The increased air pressure in the  pleural cavity  may result in the collapse of the lung.  It could be caused due to the penetrating  thoracic wound,  spontaneous rupture of  pulmonary  bulla (spontaneous pneumothorax),  fractures rib,  anaesthetist’s  needle  puncturing the pleura during stellate ganglion  block,  in making a  loin incision  to expose kidney, to perfom  adrenalctomy or  to drain a  subphrenic abcess.

Tension pneumothorax is  a condition in which  the ruptured tissues of thoracic wall  form  a  valve  that permits  air to enter the pleural cavity upon  inspiration, but does not  allow  air to  escape during expiration and therefore  greatly increases the  pressure  inside and pushing the mediastinal  structures to the opposite side

d. Pleural effusions: The excessive accumulation of fluid  in the pleural cavity is called pleural effusion. It  is usually  due to inflammation of the pleura. The  progressive  accumulation of fluid  may cause retraction  of lung towards the   hilum and may  displace the  mediastinum to the opposite side. The fluid may be in the form of:

  • Blood – Haemothorax
  • Pus – Pyothorax/empyema
  • Lymph – Chylothorax

Nerve Supply of Pleura

Q.  Which nerves supply pleura?

A. Nerve supply of pleura:

  • Parietal pleura: is pain sensitive
    • Costal and peripheral part of diaphragmatic pleura are supplied by Intercostal nerves
    • Mediastinal and central part of diaphragmatic pleura are supplied by Phrenic nerve
  • Visceral pleura: Is insensitive to pain.
    • Is supplied by autonomic (sympathetic ) nerves –T2 –T5.

In inflammation of the mediastinal and central part of diaphragmatic pleura, the pain is referred to the root of neck and the shoulder region as these parts of pleura are supplied by phrenic nerve (C3,C4,C5) and the skin at the above mentioned sites is innervated by  the same spinal segments via supraclvicular nerves (c3, C4). When  lower costal or peripheral part of diaphragmatic pleura are affected, the pain may be referred to the anterolateral abdominal wall along the distribution of lower intercostal nerves which also innervate the anterior abdominal wall.

 

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