. Principles of modern biology. Biology. 360 - Multicellular Animals, Especially Man If removed from the body, the lung shrinks down into a relatively small spongy mass. Such a deflated lung may be reinflated through the trachea—in which case the walls become stretched like those of a toy balloon. But if the inflation pressure is released, the elasticity of the stretched pulmonary walls again deflates the lung, expelling most of its content of air. The free transit of air to and from the lungs is assured by the fact that the walls of the larynx, trachea, bronchi, and larger bron- chioles are r
. Principles of modern biology. Biology. 360 - Multicellular Animals, Especially Man If removed from the body, the lung shrinks down into a relatively small spongy mass. Such a deflated lung may be reinflated through the trachea—in which case the walls become stretched like those of a toy balloon. But if the inflation pressure is released, the elasticity of the stretched pulmonary walls again deflates the lung, expelling most of its content of air. The free transit of air to and from the lungs is assured by the fact that the walls of the larynx, trachea, bronchi, and larger bron- chioles are reinforced with cartilage, which prevents the passages from collapsing (Fig. 19-3). In the trachea and bronchi the carti- laginous reinforcements take the form of a series of incomplete rings, or bands. But the larynx, which houses the vocal cords, is strengthened by a larger single encasement of cartilage (Fig. 19-3). Fach lung is covered externally by a smooth epithelium, which is called the pleura; and there is also a pleural lining on the inner surface of the thorax wall (Fig. 19-3). Thus between the two layers of the pleura there exists, at least potentially, a cavity, called the pleural cavity. Normally the pleural cav- ity is practically obliterated by the fact that the outer surface of the lung lies in intimate contact with the inner surface of the thoracic wall. However, if the pleural linings become inflamed, as in pleurisy, fluid tends to accu- mulate in the pleural cavity. The pleural cavity has no communication with the outside atmosphere. Above and to the sides it is bounded by the body wall, and below, the pleural cavity is walled off from the abdominal cavity by the diaphragm, a strong dome-shaped sheet of muscle tissue (Fig. 19-3). Pressure in the pleural cavity is generally negative (that is, less than the pres- sure of the outside atmosphere), because the. Inspiration Fig. 19-5. Manner in which the volume of the chest cavity is increased during an inspiratio
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Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectbiology
