Respiratory Physiology

Respiratory Physiology - forceful inhalations During...

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Respiratory Physiology Pleurae and Pleural Fluid Recall that the wall of the thoracic cavity is covered with parietal pleura while the surface of the lungs is covered with visceral pleura. These membranes secrete pleural fluid into the pleural cavity between the visceral and parietal membranes. This fluid reduces friction during ventilation and helps prevent the spread of infection by surrounding the lungs with a barrier. The fluid also assists in lung inhalation. During inhalation, the lifting of the thoracic wall (and associated parietal pleura) results in the movement of visceral pleura (and lung tissue), thus increasing the volume of the lungs. Inspiration and Expiration Inspiratory Muscles Several muscle aid in inspiration, which is dependent upon increasing the volume of the thoracic cavity. When the diaphragm contracts, it shifts downwards, enlarging the volume of the thoracic cavity. The scalenes and external intercostals raise the ribs during deep breathing while the pectoralis minor, sternocleidomastoid and erector spinae muscles are engaged during extremely
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Unformatted text preview: forceful inhalations. During inhalation, the abdominal muscles must relax. Expiratory Muscles A quiet expiration is accomplished by the relaxation of the inspiratory muscles and the natural elasticity of the lungs and thoracic cage. Forceful exhalation requires the contraction of the internal intercostal muscles to depress the ribs while contraction of the abdominal muscles increases abdominal pressure and forces the diaphragm upward. Laws of Gas Behavior The movement of air into and out of the lungs is driven by the differences between atmospheric pressure and intrapulmonary pressure. These pressure gradients are created by changes in the volume of the thoracic cavity and lungs. As with other "solutes", air flows down its pressure gradient. Several principles govern the behavior of gases; these are collectively known as the Gas Laws. The ones most important for respiratory physiology are Boyle's Law, Charles' Law, Dalton's Law and Henry's Law (see Table 1 )....
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