TAILIEUCHUNG - Ebook Guyton and hall textbook of medical physiology (13/E): Part 2

(BQ) Part 2 book "Guyton and hall textbook of medical physiology" has contents: Respiration; aviation, space, and deep sea diving physiology; gastrointestinal physiology; metabolism and temperature regulation; sports physiology, and other contents. | CHAPTER 3 8  The main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide. The four major components of respiration are (1) pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the lung alveoli; (2) diffusion of oxygen (O2) and carbon dioxide (CO2) between the alveoli and the blood; (3) transport of oxygen and carbon dioxide in the blood and body fluids to and from the body’s tissue cells; and (4) regulation of ventilation and other facets of respi­ ration. This chapter is a discussion of pulmonary ven­ tilation, and the subsequent five chapters cover other respiratory functions plus the physiology of special respi­ ratory abnormalities. MECHANICS OF PULMONARY VENTILATION MUSCLES THAT CAUSE LUNG EXPANSION AND CONTRACTION The lungs can be expanded and contracted in two ways: (1) by downward and upward movement of the dia­ phragm to lengthen or shorten the chest cavity, and (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity. Figure 38-1 shows these two methods. Normal quiet breathing is accomplished almost entirely by the first method, that is, by movement of the dia­ phragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of the lungs downward. Then, during expiration, the diaphragm simply relaxes, and the elastic recoil of the lungs, chest wall, and abdominal struc­ tures compresses the lungs and expels the air. During heavy breathing, however, the elastic forces are not pow­ erful enough to cause the necessary rapid expiration, so extra force is achieved mainly by contraction of the abdominal muscles, which pushes the abdominal con­ tents upward against the bottom of the diaphragm, thereby compressing the lungs. The second method for expanding the lungs is to raise the rib cage. Raising the rib cage expands the lungs because, in the natural resting position, the ribs slant downward, as shown on .

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