Chapter 3

### Big Picture

The lungs exchange oxygen and carbon dioxide and are the functional organs of the respiratory system. To serve that vital function, the lungs are located adjacent to the heart within the pleural sacs. The pleurae are serous membranes that line the internal surface of the thoracic cage and the outside surface of the lungs. The plurae secrete fluid that decreases resistance against lung movment during breathing.

### Description of Pleural Sacs

Each lung (right and left) is contained within a serous membrane called the pleural sac (Figure 3-1A). The right and left pleural sacs occupy most of the thoracic cavity and flank both sides of the heart. Each pleural sac is composed of two layers of serous (secretory) membrane, the parietal pleura and the visceral pleura (Figure 3-1B).

• Parietal pleura. The external serous membrane lining the internal surface (wall) of the thoracic cavity.
• Visceral pleura. The internal serous membrane intimately attached to the surface of each lung.
• Pleural fluid. A layer of fluid located between the parietal and visceral pleurae in what is called the pleural space.

###### Figure 3-1

A. Pleura sacs in situ. B. Step dissection of lateral thoracic wall from skin to the lungs. Pleura in coronal (C) and axial (D) sections.

### Regions of the Parietal Pleura

As previously described, the parietal pleura lines the internal surface (wall) of the thoracic cavity, including the lateral sides of the mediastinum (Figure 3-1C and D). The parietal pleura is separated from the thoracic wall by the endothoracic fascia, a thin layer of connective tissue located between the parietal pleura and the innermost intercostal muscles and membrane. The parietal pleura is assigned specific names, depending on the structures that it lines.

• Mediastinal parietal pleura. Lines the lateral surface of the mediastinum (the space between the lungs where the heart is located).
• Costal parietal pleura. Lines the internal surface of the ribs.
• Diaphragmatic parietal pleura. Lines the superior surface of the diaphragm.
• Cervical parietal pleura (cupula). Extends above rib 1 to the root of the neck.

### Innervation and Vascular Supply of the Parietal Pleura

Intercostal nerves supply the costal parietal pleura and the peripheral portion of the diaphragmatic parietal pleura. Phrenic nerves supply the central portion of the diaphragmatic parietal pleura and the mediastinal parietal pleura. The parietal pleura is innervated by general sensory neurons, and therefore, it is sensitive to pain.

The parietal pleura receives its vascular supply via branches of the internal thoracic, superior phrenic, posterior intercostal, and superior intercostal arteries.

### Visceral Pleura

The visceral pleura is intimately attached to each lung and follows ...

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