The Pleurae

The surface of the lung is covered by a serous membrane, the visceral pleura (PLOOR-uh), which extends into the fissures. At the hilum, the visceral pleura turns back on itself and forms the parietal pleura, which adheres to the mediastinum, superior surface of the diaphragm, and inner surface of the rib cage (see fig. 22.9b). An extension of the parietal pleura, the pulmonary ligament, extends from the base of each lung to the diaphragm. The space between the parietal and visceral pleurae is called the pleural cavity. The two membranes are normally separated only by a film of slippery pleural fluid; thus, the pleural cavity is only a potential space, meaning there is normally no room between the membranes, but under pathological conditions this space can fill with air or liquid.

The pleurae and pleural fluid have three functions:

1. Reduction of friction. Pleural fluid acts as a lubricant that enables the lungs to expand and contract with minimal friction. In some forms of pleurisy, the pleurae are dry and inflamed and each breath gives painful testimony to the function that the fluid should be serving.

2. Creation of pressure gradient. Pressure in the pleural cavity is lower than atmospheric pressure; as explained later, this assists in inflation of the lungs.

3. Compartmentalization. The pleurae, mediastinum, and pericardium compartmentalize the thoracic organs and prevent infections of one organ from spreading easily to neighboring organs.

_Think About It_

In what ways do the structure and function of the pleurae resemble the structure and function of the pericardium?

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

850 Part Four Regulation and Maintenance

Pulmonary Ligament Cadaver

Thoracic vertebra Spinal cord

Ribs

Visceral pleura Parietal pleura

Figure 22.9 Gross Anatomy of the Lungs. (a) Anterior view. (b) Cross section through the thorax of a cadaver showing the heart, lungs, and pleurae.

Thoracic vertebra Spinal cord

Ribs

Visceral pleura Parietal pleura

Figure 22.9 Gross Anatomy of the Lungs. (a) Anterior view. (b) Cross section through the thorax of a cadaver showing the heart, lungs, and pleurae.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

1. A dust particle is inhaled and gets into an alveolus without being trapped along the way. Describe the path it takes, naming all air passages from external naris to alveolus. What would happen to it after arrival in the alveolus?

2. Describe the histology of the epithelium and lamina propria of the nasal cavity and the functions of the cell types present.

3. Describe the roles of the intrinsic muscles, corniculate cartilages, and arytenoid cartilages in speech.

4. Contrast the epithelium of the bronchioles with that of the alveoli and explain how the structural difference is related to their functional differences.

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Responses

  • Vilho
    How are the lungs compartmentalized by the pleural membranes?
    4 years ago

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