ANATOMY OF PLEURA Dr. Mujahid Khan

Location The pleurae and lungs lie on either side of the mediastinum within the chest cavity Each pleura has two parts: Parietal layer Visceral layer

Parietal Layer It lines the thoracic wall Covers the thoracic surface of the diaphragm and the lateral aspect of the mediastinum Extends into the root of the neck to line the undersurface of the suprapleural membrane at the thoracic outlet

Visceral Layer It completely covers the outer surfaces of the lungs Extends into the depths of the interlobar fissures

Pleural Cuff The two layers continuous with one another by means of a cuff of pleura This cuff surrounds the structures entering and leaving the lung at the hilum of each lung Pleural cuff hangs down as a loose fold called the pulmonary ligament

Pleural Cavity The parietal and visceral layers are separated from one another by a slitlike space called pleural cavity Clinicians use the term pleural space instead of the anatomic term pleural cavity Pleural cavity contains thin film of tissue fluid called pleural fluid Fluid permits the two layers to move on each other with the minimum of friction

Cervical Pleura Parietal pleura is divided into the region in which it lies or the surface that it covers The cervical pleura extends up into the neck It lines 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

Costal Pleura It lines the inner surfaces of: The ribs The costal cartilages The intercostal spaces The sides of the vertebral bodies The back of the sternum

Diaphragmatic Pleura It covers the thoracic surface of the diaphragm In quiet respiration, the costal and diaphragmatic pleurae are in apposition to each other below the lower border of the lung Costal and diaphragmatic pleurae separate in deep inspiration

Costodiaphragmatic Recess The lower area of the pleural cavity into which the lung expands on inspiration is referred to as the costodiaphragmatic recess

Mediastinal Pleura It covers and forms the lateral boundary of the mediastinum It is reflected as a cuff around the vessels and bronchi at the hilum of the lung Then continuous with the visceral pleura Each lung lies free except at the hilum it is attached to the blood vessels and bronchi that constitute the lung root

Mediastinal Pleura During full inspiration the lungs expand and fill the pleural cavities During quiet inspiration the lungs do not fully occupy the pleural cavities at four sites The right and left costodiaphragmatic recesses The right and left costomediastinal recesses

Costodiaphragmatic recesses Are slitlike spaces between the costal and diaphragmatic parietal pleurae Separated only by a capillary layer of pleural fluid During inspiration, the lower margins of the lungs descend into the recesses During expiration, the lower margins of the lungs ascend so that the costal and diaphragmatic pleurae come together again

Costomediastinal Recesses Are situated along the anterior margins of the pleura They are slitlike spaces between the costal and the mediastinal parietal pleurae Separated by a capillary layer of pleural fluid During inspiration and expiration, the anterior borders of the lungs slide in and out of the recesses

Nerve Supply The parietal pleura is sensitive to pain, temperature, touch and pressure, and is supplied as follows: The 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 The visceral pleura covering the lungs is sensitive to stretch It is insensitive to common sensations such as pain and touch It receives an autonomic nerve supply from the pulmonary plexus

Pleural Fluid The pleural space normally contains 5 to 10 ml of clear fluid It lubricates the opposing surfaces of the visceral and parietal pleurae during respiration The formation of the fluid results from hydrostatic and osmotic pressures between the capillaries The pleural fluid is normally absorbed into the capillaries of the visceral pleura

Pleural Fluid Any condition that increases the production of the fluid or impairs the drainage of the fluid results in the abnormal accumulation of fluid, called pleural effusion The presence of 300 ml of fluid in the costodiaphragmatic recess in an adult is sufficient to enable its clinical detection The clinical signs include decreased lung expansion on the side of the effusion, with decreased breath sounds and dullness on percussion over the effusion

Pleuricy Inflammation of the pleura secondary to inflammation of the lung called pneumonia Pleural surfaces become coated with inflammatory exudate, causing the surfaces to be roughened Produces friction, and a pleural rub It can be heard with the stethoscope on inspiration and expiration

Pleuricy Often the exudate becomes invaded by fibroblasts That lay down collagen and bind the visceral pleura to the parietal pleura Forms pleural adhesions