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The reader states the functions of the respiratory system and relates the structural organization of the system to its functions.

  • Describes the exchange of oxygen and carbon dioxide with the atmosphere and relates gas exchange to the metabolism of the tissues of the body.

  • Defines the role of the respiratory system in acid-base balance.

  • Lists the nonrespiratory functions of the lungs.

  • Defines and describes the alveolar-capillary unit, the site of gas exchange in the lungs.

  • Describes the transport of gas through the conducting airways to and from the alveoli.

  • Describes the structural characteristics of the airways.

  • Lists the components of the chest wall and relates the functions of the muscles of respiration to the movement of air into and out of the alveoli.

  • Describes the central nervous system initiation of breathing and the innervation of the respiratory muscles.

imageThe main functions of the respiratory system are to obtain oxygen from the external environment and supply it to the cells and to remove from the body the carbon dioxide produced by cellular metabolism.

The respiratory system is composed of the lungs, the conducting airways, the parts of the central nervous system concerned with the control of the muscles of respiration, and the chest wall. The chest wall consists of the muscles of respiration—such as the diaphragm, the intercostal muscles, and the abdominal muscles—and the rib cage.


imageThe functions of the respiratory system include gas exchange, acid-base balance, phonation, pulmonary defense and metabolism, and the handling of bioactive materials.

Gas Exchange

Oxygen from the ambient air is exchanged for carbon dioxide produced by the cells of the body in the alveoli of the lungs. Fresh air, containing oxygen, is inspired into the lungs through the conducting airways. The forces causing the air to flow are generated by the respiratory muscles, acting on commands initiated by the central nervous system. At the same time, venous blood returning from the various body tissues is pumped into the lungs by the right ventricle of the heart. This mixed venous blood has a high carbon dioxide content and a low oxygen content. In the pulmonary capillaries, carbon dioxide is exchanged for oxygen from the alveoli. The blood leaving the lungs, which now has a high oxygen content and a relatively low carbon dioxide content, is distributed to the tissues of the body by the left side of the heart. During expiration, gas with a high concentration of carbon dioxide is expelled from the body. A schematic diagram of the gas exchange function of the respiratory system is shown in Figure 1–1.

Figure 1–1

Schematic representation of gas exchange between the tissues of the body and the environment.

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