8. Anatomy of Pleura.pdf

ANATOMY OF THE PLEURA - Pleura, like peritoneum is a serous membrane, which is lined by mesothelium, which secretes a watery lubricant – the serous fluid - There are two pleural sacs, one on each side of the mediastinum - Each...

ANATOMY OF THE PLEURA - Pleura, like peritoneum is a serous membrane, which is lined by mesothelium, which secretes a watery lubricant – the serous fluid - There are two pleural sacs, one on each side of the mediastinum - Each pleural sac is invaginated from its medial side by the lung, so that it has an outer layer, parietal pleura, and an inner layer, the visceral or pulmonary pleura - The two layers are continuous with each other around the hilum of the lung, and enclose a potential space called pleural cavity STRUCTURE ASSOCIATED LAB/ LECTURE Pleura has two layers: 1. Inner Visceral Layer 2. Outer Parietal Layer Inner Visceral Layer - It invests all the surfaces of the lung, except at the hilum and along the attachment of pulmonary ligament - It also extends into the depths of the fissures of the lungs - It is firmly adherent to the lung surface and cannot be separated from it Outer Parietal Layer - The parietal layer is thicker than the visceral layer and lines the pulmonary cavity (i.e. thoracic cavity and mediastinum) - The space between the two layers is called pleural cavity For the purpose of description, the parietal pleura is divided according to the regions it covers or lines into: I. Costal pleura II. Diaphragmatic pleura III. Mediastinal pleura IV. Cervical pleura I. Costal Pleura - Lines the inner surface of the thoracic wall, but separated from it by endothoracic fascia. II. Diaphragmatic Pleura - Covers the superior surface of the diaphragm III. Mediastinal Pleura - Lines the corresponding surface of the mediastinum and forms its lateral boundary. - Over the root of the lung, it becomes continuous with the visceral pleura IV. Cervical Pleura - It is the dome of parietal pleura which extends into the root of the neck. - It is called cupola and covers the apex of the lung, hence care should be taken while penetrating this area with anesthetic needle. - It is covered by suprapleural membrane or Sibson’s fascia. PULMONARY LIGAMENT - After surrounding the root of the lung, the pleura extends down as a fold called pulmonary ligament - It extends from the root of the lung as far down as the diaphragm between the lung and the mediastinum. - This fold is filled with loose areolar tissue and contain few lymphatics Functions: - It provides dead space for the expansion of inferior pulmonary vein during high venous return as in exercise - It allows the descent of the root of the lung with the descent of the diaphragm during inspiration Surface Marking of Pleura Knowledge of reflection of parietal pleura on the surface of the chest wall is of great importance while carrying out various medical and surgical procedures The reflection of parietal pleura can be marked on the surface by following lines: Cervical Pleura - Marked by a curved line (convexity directed upwards) drawn from sternoclavicular joint to the junction of medial third and middle third of the clavicle. - The summit of the dome of pleura lies 1 inch above the medial one- third of the clavicle. Anterior (costomediastinal) line of pleural reflection: On the right side: - It extends downwards and medially from the right sternoclavicular joint to the midpoint of the sternal angle, then descends vertically up to the midpoint of the xiphisternal joint On the left side: - It extends downwards and medially from the left sternoclavicular joint to the midpoint of the sternal angle, then descends vertically only up to the level of the 4th costal cartilage. - It then arches outwards to reach the lateral margin of the sternum and then it runs downwards a short distance lateral to this margin to reach the 6th costal cartilage about 3cm from the midline leaving a part of pericardium directly in contact with the anterior chest wall (bare area of heart) Inferior (costomediastinal) line of pleural reflection: It passes laterally around the chest wall from the lower limit of the anterior line of pleural reflection. It differs slightly on two sides: On the right side: - The line of pleural reflection starts from the xiphisternal joint or behind the xiphoid process and crosses: - the 8th rib in the midclavicular line - 10th rib in the midaxillary line - 12th rib at the lateral border of the erector spinae muscle, 2cm lateral to the spine of T12 On the left side: - The line of pleural reflection starts at the level of the 6th costal cartilage, about 2cm lateral to the midline. - Thereafter it follows the same course as on the right side Posterior (costovertebral) line of pleural reflection: - It ascends from the end of the inferior line, 2 cm lateral the T12 spine along the vertebral column to the point, 2 cm lateral to the spine of C7 vertebra. The costal pleura becomes mediastinal pleura along this line - The inferior margin of the lung passes more horizontally than the inferior margin of the pleura. - Consequently, it crosses: - the 6th rib in the midclavicular line - 8th rib in the midaxillary line - 10th rib at the lateral border of the erector spinae muscle - The ribs crossed by the inferior margin of the lung and pleura in the midclavicular line, midaxillary line and lateral to erector spinae muscle are compared below - Inferior margin of lung 6th rib, 8th rib, 10th rib - Inferior margin of pleura 8th rib, 10th rib, 12th rib PLEURAL RECESSES are the regions/spaces in the pleural cavity which are not occupied by lungs during quite respiration They lie between the two folds of parietal pleura I. Costomediastinal Recess - Lies anteriorly behind the sternum and costal cartilages, between the costal and mediastinal pleura - Prominent in the cardiac notch of the lung - This recess, except in the cardiac notch region is occupied by anterior margin of lung even during quite respiration II. Costo-diaphrgmatic Recess - Lies inferiorly between the costal and diaphragmatic pleurae. The line of this reflection is two ribs lower than the lower border of the lung. - So this recess is not filled by lung during quiet inspiration and is partially filled by lung during deep inspiration. - This is the first part of the pleural cavity to be filled up by the pleural effusions NERVE, BLOOD & LYMPHATICS Parietal pleura - develops from somatopleuric layer of lateral plate mesoderm - Supplied by somatic nerves – intercostal and phrenic nerve - Costal and peripheral part of diaphragmatic pleura are supplied by intercostal and phrenic nerves - Mediastinal and central part of diaphragmatic pleurae are supplied by phrenic nerve - Parietal pleura is pain sensitive - Arterial supply is by branches from the intercostal, internal thoracic and musculophrenic arteries - Veins drain into azygos and internal thoracic veins - Lymphatics drain into intercostal, internal mammary, posterior  mediastinal and diaphragmatic nodes Pulmonary Pleura - develops from splanchnopleuric layer of lateral plate mesoderm - Supplied by autonomic (sympathetic) nerves (T2-T5), which accompany the bronchial vessels - Pulmonary pleura is pain insensitive - Blood supply is by bronchial vessels - Lymphatics drain into bronchopulmonary lymph nodes FUNCTIONAL IMPORTANCE OF PLEURAL CAVITY - Pleural cavity is a potential space. - The opposed surfaces of parietal and visceral pleura are lined by mesothelial cells. - They secrete a small quantity of serous fluid into the space continuously which is essential for the movement of the lungs (to prevent rubbing during lung movements). - A negative pressure is maintained inside the pleural cavity which is necessary to retain visceral pleura in contact with parietal pleura. - If there is positive pressure (i.e., pneumothorax) inside the pleural cavity, the inherent elastic recoil of the lung tissue pulls the visceral pleura away from the parietal pleura causing the collapse of the lung. CLINICAL CORRELATION 1. Costo-diaphragmatic recess: - Lies inferiorly between the costal and diaphragmatic pleurae - This is the first part of the pleural cavity to be filled up by the pleural effusions NB: The costodiaphragmatic recess can be entered through the 9th and 10th intercostal spaces without penetrating the lung in patient with quite breathing because lung lies opposite 8th-10th ribs. Inflammation of the pleura is called Pleurisy or pleuritis. It is commonly caused by pulmonary tuberculosis. Pleural cavity may contain: 1. Pneumothorax - air in the pleural cavity 2. Hydrothorax – fluid in the pleural cavity 3. Hydropneumothorax – fluid with air in the pleural cavity 4. Haemothorax – blood in the pleural cavity 5. Empyema – pus in the pleural cavity 2. Shoulder Tip Pain - The pain from central diaphragmatic pleura and mediastinal pleura is referred to the neck or shoulder through phrenic nerve (C3, C4, C5) because skin at these sites has same segmental supply through the supraclavicular nerves (C3, C4, C5).