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The lungs (functional organs of the respiratory system) are located within serous membranes that line the inside of the rib cage (parietal pleura) and outside of the lungs (visceral pleura).
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The pleurae secrete fluid that decreases resistance against lung movement during breathing.
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DESCRIPTION OF PLEURAL SACS
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Each lung (right and left) is contained within a serous membrane called a pleural sac. The pleural sacs flank both sides of the heart and occupy most of the thoracic cavity. Each pleural sac is composed of two serous layers: the parietal pleura and visceral pleura (Figure 3-1A and B).
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Parietal pleura lines the internal surface of the thoracic cavity. The endothoracic fascia is a thin layer of connective tissue that adheres the parietal pleura to the internal thoracic wall (Figure 3-1B–D).
Regions. The parietal pleura is assigned specific names, depending on the area it lines:
Mediastinal parietal pleura. Lines the lateral surface of the mediastinum (location of the pericardium and heart).
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. The parietal pleura on each side is associated with the body wall (i.e., skin and IC muscles) and thus innervated by general sensory neurons (therefore sensitive to pain). The nerves that provide sensory innervation are (Figure 3-1B):
Intercostal nerves. Innervate the parietal pleura lining the peripheral portion of the diaphragm and the ribs.
Phrenic nerves. Innervate the parietal pleura lining the central portion of diaphragm and the mediastinum.
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The visceral pleura surrounds and is intimately attached to each lung and follows the contour of the lobes; the visceral pleura is contiguous with the parietal pleura at the hilum of each lung (Figure 3-1B–D).
Function. The visceral pleura along with the parietal pleura produce and reabsorb pleural fluid; the bulk of pleural fluid is cleared by lymphatics in the parietal pleura.
Innervation. The visceral pleura is associated with the organ (lung) and thus innervated by visceral sensory neurons (therefore insensitive to pain) from the autonomic vagus nerve (CN X).
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The pleural space is located between the parietal and visceral pleurae. Because the pericardium and heart occupy the mediastinum, the right and left pleural spaces do not communicate.