Pleura is a serous membrane covering the lung. There are two layers of pleura:-
- Visceral (pulmonary) pleura intimately invest the lungs and are developed from splanchnopleuric lateral mesoderm.
- Parietal pleura is developed from somatopleuric lateral mesoderm. Parietal pleura is divided into 4 parts
- Cervical (dome)
Lines of pleural reflection are-
- Lower border (Costodiaphragmatic line of pleural reflection):- Starts at xiphisternal joint, crosses mid clavicularline at 8th rib and midaxillary line at 10th rib and ends posteriorly 2cm lateral to spinous process ofT12 vertebra.
- Anterior border (costomediastinalline of pleural reflection):- It differs on right and left side.
- Right side:-Beginning from sternoclavicular joint, it descends downwards and medially to reach sternal angle close to mid line and further extends up toxiphisternal joint (up to6thsternochondraljoint) in midline.
- Left side:-Beginning from sternoclavicular joint, it descends downward and medially to sternal angle and then descends vertically close to midline up to 4thrib. Below this level it deviates away from midline lying lateral (2-15 mm) to sternal margin to reach the 6thsternochondral junction. This deviation is known as cardiac notch of pleura. Due to this, the left half of lower part of body of sternum is directly related to' pericardium without intervening pleural sac. This area is known as superficial area of cardiac dullness.
- Posterior border: - Extends from a point 2 cm lateral to 7thcervical vertebra to a point 2 cm lateral to the 12ththoracic vertebra.
Recesses of the pleura
These act as reserve spaces for expansion of lungs during deep inspiration. There are two such recesses.
- Costodiaphragmatic recess
- It lieslnferiorlybetween costal and diaphragmatic parietal pleura. The recess is 9cm deep in midaxillary line (maximum), 5 cm in scapular line posteriorly and 4 cm in midclavicular line (minimum). This is the first part of pleural cavity to be filled by pleural fluid in pleural effusion. Vertically it extends from 8th to 10th rib in mid axillary line.
- Costomediastinal Recess
- It lies anteriorlybetween costal and mediastina parietal pleural (behind sternum and costal cartilage). The left recess is potentially larger because of cardiac notch in left lung. The recess is filled by anterior margin of left lung even during quite breathing.
- Parietal pleura is pain sensitive- and is supplied by intercostal and phrenic nerves. The costal and peripheral part of diaphragmatic pleura is supplied by intercostal nerves and the mediastinal and central part of diaphragmatic pleura is supplied by phrenic nerve.
- Pulmonary (visceral) pleura is pain insensitive and is innervated by autonomic nerves (sympathetic from T2 -T5 spinal nerves and parasympathetic from vagus).