Answer:
C
Explanation:
The two lungs and their pleural sacs are situated in the thoracic cavity (figs. 22-1 and 22-2). The pleura is a thin, glistening, slippery serous membrane, inflammation of which is called pleurisy. The pleura lines the thoracic wall and diaphragm, where it is known as the parietal pleura. It is reflected onto the lung, where it is called the visceral pleura. The visceral pleura covers the lung and dips into its fissures. The facing surfaces of the parietal and visceral pleurae slide smoothly against each other during respiration. The contact between the parietal and visceral pleurae depends on the atmospheric pressure (1) on the outside of the chest wall and (2) inside the alveoli (which are connected to the exterior by the bronchial tree). On the other hand, the two pleural layers tend to be separated by the elasticity of (1) the thoracic wall (directed outward) and (2) the lungs (stretched by inspiration). The pleural cavity, which is the potential space between the two layers, contains only a thin film of fluid. Air in the pleural cavity (pneumothorax) results in collapse of the lung. The pleura is supplied by adjacent arteries and nerves and has numerous lymphatics. Irritation of the parietal pleura causes pain referred to the thoraco-abdominal wall (intercostal nerves) or to the shoulder (phrenic nerve).
The parietal pleura has costal, mediastinal, and diaphragmatic parts and a cupola (fig. 22-3). The costal pleura is separated from the sternum, costal cartilages, ribs, and muscles by a loose connective tissue termed endothoracic fascia, which provides a natural cleavage plane for surgical separation of the pleura from the thoracic wall. Anteriorly, the costal pleura turns sharply onto the mediastinum, and the underlying portion of the pleural cavity is called the costomediastinal recess. Inferiorly, the costal pleura is continuous with the diaphragmatic pleura, and the underlying space is termed the costodiaphragmatic recess. In the adult, the anterior borders of the right and left pleurae probably meet at or near the median plane during a part of their course. The left anterior border sometimes diverges to leave a part of the pericardium uncovered (bare area). Posteriorly, the pleura crosses the twelfth rib. At the root of the lung, the mediastinal pleura turns laterally, enclosing the structures at the root and becoming continuous with the visceral pleura. This reflection projects downward as a tapering double fold called the pulmonary ligament. The mediastinal pleura is adherent to the pericardium except where the phrenic nerve descends between them. Above the arch of the aorta, the right and left pleurae approach each other behind the esophagus. The diaphragmatic pleura covers most of the diaphragm except the central tendon. The cupola (or cervical pleura) is the continuation of the costal and mediastinal parts of the pleura over the apex of the lung. The cupola is strengthened by a thickening of the endothoracic fascia termed the suprapleural membrane, which is attached to the inner margin of the first rib and the transverse process of the seventh cervical vertebra (C7). Some muscular fibers (scalenus minimus) may be inserted into the membrane. Because of the slope of the first rib, the cupola of the pleura and the apex of the lung project upward into the neck, posterior to the sternomastoid, and hence may be injured in wounds of the neck. Their highest point is 2 to 3 cm or more above the level of the medial third of the clavicle. The sympathetic trunks and first thoracic nerves are found posterior to the cupola.
The anterior border of the pleura extends downward from the cupola, passing posterior to the sternoclavicular joint, then to the middle of the sternal angle, and next to approximately the level of the xiphisternal joint. The inferior border of the pleura extends laterally from the xiphisternal joint, crosses rib 8 in the midclavicular line and rib 10 in the midaxillary line, and then proceeds toward the spine of the 12th thoracic vertebra (see fig. 22-2). Considerable individual variation occurs, but generally the pleura extends two fingerbreadths inferior to the lung.
