THE PLEURA | Structure and features of pleura of lungs | Medicoze

The pleura is a fibroelastic serous membrane lined by squamous epithelium forming a sac on each side of the chest. Each pleural sac is a closed cavity invaginated by a lung. Parietal pleura lines the chest wall and visceral (pulmonary) pleura covers the lungs. These two pleural layers are continuous around the root of the lung and are separated by a thin film of serous fluid, permitting them to glide easily on each other. The layers are prevented from separating by the fluid’s surface tension and the negative pressure in the thoracic cavity.Thus, when the thoracic cage expands, the lung also must expand and air is inhaled. Parietal pleura lines the ribs, costal cartilages, intercostal spaces, lateral surface of the mediastinum and upper surface of the diaphragm. Superiorly, it extends above the thoracic inlet into the neck as the cervical dome of pleura; inferiorly, around the margin of the diaphragm, it forms a narrow gutter, the costodiaphragmatic recess; anteriorly, the left costal and mediastinal surfaces are in contact, extending in front of the heart to form the costomediastinal recess. Mediastinal pleura invests the main bronchi and pulmonary vessels and passes on to the surface of the lung to become visceral pleura, which covers the lung and extends into its interlobar fissures. The surface markings of the pleural sacs should be noted. On both sides, the upper limit lies about 3 cm above the medial third of the clavicle. From here, the lines of pleural reflections descend behind the sternoclavicular joints to almost meet in the midline at the level of the 2nd costal cartilage. At the 4th costal cartilage, whereas the left pleura deviates laterally and descends along the lateral border of the sternum to the 6th costal cartilage, the right pleural reflection continues down, near to the midline, to the 6th costal cartilage. At this point, on both sides, the pleural reflections pass laterally behind the costal margin to reach the 8th rib in the midclavicular line and the 10th rib in the midaxillary line, and along the 12th rib and the paravertebral line. Visceral pleura has no pain fibres, but the parietal pleura is richly supplied by branches of the somatic intercostal and phrenic nerves. Lymph from the pulmonary pleura passes to a superficial plexus in the lung and then to the hilar nodes. Parietal pleura drains to the parasternal, diaphragmatic and posterior mediastinal nodes.