PLEURA AND PLEURAL CAVITY

PLEURA AND PLEURAL CAVITY

PLEURAPleural cavity is lined by single layer of flat cells, mesothelium and an associated layer of supporting connective tissue; together they form pleura.

PLEURAparietal pleura :pleura associated with the walls of a pleural cavity visceral pleura :pleura, which adheres to and covers the lung: reflects from the medial wall and onto the surface of the lung

DEVELOPMENT OF PLEURAeach lung bud invaginates the wall of coelomic cavity and then grows to fill a greater part of the cavitylung is covered with visceral pleura and the thoracic wall is lined with parietal pleuraoriginal coelomic cavity is reduced to slitlike space called the pleural cavity as a result of the growth of the lung.

SUPRAPLEURAL MEMBRANE

thickening of connective tissue that covers the apex of lungextension of endothoracic fascia that exists between parietal pleura and thoracic cageextends between inner border of first rib and transverse process of C7 vertebraact as a rigid barrier so as to prevent changes in intrathoracic pressure drawing upon the contents of the neck

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PARTS OF PARIETAL PLEURAcostal part diaphragmatic partmediastinal partcervical pleura

CUPOLA OR CERVICAL PARTthe dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity cervical pleura extends up into the neck, lining the undersurface of the suprapleural membrane It reaches a level 1 to 1.5 in. (2.5 to 4 cm) above the medial third of the clavicle

MEDIASTINAL PARTpleura covering the mediastinum

COSTAL PARTpleura related to the ribs and intercostal spaces

DIAPHRAGMATIC PARTpleura covering the diaphragm

REFLECTIONS OF PARIETAL PLEURASuperiorly: pleural cavity can project as much as 3-4 cm above the first costal cartilage

Anteriorly: pleural cavities approach each other posterior to the upper part of the sternum. posterior to the lower part of the sternum, the parietal pleura does not come as close to the midline on the left side

Inferiorly: In the midclavicular line, the pleural cavity extends inferiorly to rib VIII. In the midaxillary line, it extends to rib X. From this point, the inferior margin courses horizontally, to reach vertebra XII

VISCERAL PLEURAVisceral pleura is continuous with parietal pleura at the hilum of each lung. The visceral pleura is firmly attached to the surface of the lung, including both opposed surfaces of the fissures that divide the lungs into lobes.

PULMONARY LIGAMENTThe parietal pleura surrounding the root of the lung extends downwards beyond the root as a fold called the pulmonary ligament. The fold contains a thin layer of loose areolar tissue with a few lymphatics

Actually it provides a dead space into which the pulmonary veins can expand during increased venous return as in exercise. The lung roots can also descend into it with the descent of the diaphragm

NERVE SUPPLY OF THE PLEURA The parietal pleura is sensitive to pain, temperature, touch, and pressureThe costal pleura is segmentally supplied by the intercostal nerves.The mediastinal pleura is supplied by the phrenic nerve.The diaphragmatic pleura is supplied over the domes by the phrenic nerve and around the periphery by the lower six intercostal nerves.

NERVE SUPPLY OF VISCERAL PLEURAThe visceral pleura covering the lungs is sensitive to stretch but is insensitive to common sensations such as pain and touch. It receives an autonomic nerve supply from the pulmonary plexus

BLOOD SUPPLYThe parietal pleura is supplied by intercostal, internal thoracic and musculophrenic arteries.The veins drain mostly into the azygos and internal thoracic veins. The pulmonary pleura, like the lung, is supplied by the bronchial arteries while the veins drain into bronchial veins.

LYMPHATIC DRAINAGEPARIETAL PLEURA: The lymphatics drain into the intercostal, internal mammary, posterior mediastinal and diaphragmatic nodes.VISCERAL PLEURA: It is drained by the bronchopulmonary lymph nodes.

PLEURAL CAVITYTwo pleural cavities are situated on either side of the mediastinumDuring development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura

Each lung remains attached to the mediastinum by a root formed by the airway, pulmonary blood vessels, lymphatic tissues, and nervesOnly a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity

Two pleural cavities, one on either side of the mediastinum, surround the lungssuperiorly: extend above rib I into the root of the neck inferiorly: they extend to a level just above the costal margin medialy: wall of each pleural cavity is the mediastinum

PLEURAL RECESSESThe lungs do not completely fill the anterior or posterior inferior regions of the pleural cavitiesThis results in recesses in which two layers of parietal pleura become opposed. Expansion of the lungs into these spaces usually occurs only during forced inspirationthe recesses provide potential spaces in which fluids can collect and from which fluids can be aspirated

Costomediastinal recesses: Anteriorly, where costal pleura is opposed to mediastinal pleura. The largest is on the left side in the region overlying the heart.

COSTODIAPHRAGMATIC RECESS

The largest and clinically most important recesses occur in each pleural cavity between the costal pleura and diaphragmatic pleura

The costodiaphragmatic recesses are the regions between the inferior margin of the lungs and inferior margin of the pleural cavitiesThey are deepest after forced expiration and shallowest after forced inspiration

PLEURAL FLUIDThe pleural space normally contains 5 to 10 mL of clear fluid, which lubricates the apposing surfaces of the visceral and parietal pleura during respiratory movementsThe formation of the fluid results from hydrostatic and osmotic pressures

Since the hydrostatic pressures are greater in the capillaries of the parietal pleura than in the capillaries of the visceral pleura (pulmonary circulation), the pleural fluid is normally absorbed into the capillaries of the visceral pleura.

Any condition that increases the production of the fluid (e.g., inflammation, malignancy, congestive heart disease) or impairs the drainage of the fluid (e.g., collapsed lung) results in the abnormal accumulation of fluid, called pleural effusionThe presence of 300 mL of fluid in the costodiaphragmatic recess in an adult is sufficient to enable its clinical detectionThe clinical signs include decreased lung expansion on the side of the effusion, with decreased breath sounds and dullness on percussion over the effusion

A collection of pus in the pleural cavity is called an empyemaAspiration of any fluid from the pleural cavity is called paracentesis thoracis. It is 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.

PLEURISYInflammation of the pleura (pleuritis or pleurisy), secondary to inflammation of the lung, results in the pleural surfaces becoming coated with inflammatory exudate, causing the surfaces to be roughened. This roughening produces friction, and a pleural rub can be heard with the stethoscope on inspiration and expiration.exudate becomes invaded by fibroblasts, which lay down collagen and bind the visceral pleura to the parietal pleura, forming pleural adhesions

PNEUMOTHORAXAs the result of disease or injury, air can enter the pleural cavity from the lungs or through the chest wallStab wounds of the thoracic wall may pierce the parietal pleura so that the pleural cavity is open to the outside airThis condition is called open pneumothorax

PNEUMOTHORAXIn these circumstances, the air pressure builds up on the wounded side and pushes the mediastinum toward the opposite sideIn this situation, a collapsed lung is on the injured side and the opposite lung is compressed by the deflected mediastinum. This dangerous condition is called a tension pneumothorax

Air in the pleural cavity associated with serous fluid is known as hydropneumothorax, associated with pus as pyopneumothorax, and associated with blood as hemopneumothorax

In hemopneumothorax, blood enters the pleural cavity. It can be caused by stab or bullet wounds to the chest wall, resulting in bleeding from blood vessels in the chest wall, from vessels in the chest cavity, or from a lacerated lung

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