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SECTION VI: RESPIRATORY PHYSIOLOGY: INTRODUCTION

The uptake of O2 and removal of CO2 from the body is the primary goal of the lung. At rest, a normal human breathes 12–15 times a minute. With each breath containing ~500 mL of air, this translates to 6–8 L of air that is inspired and expired every minute. On average, 250 mL of O2 enters the body per minute and 200 mL of CO2 is excreted. In addition to the O2 that enters the respiratory system, inspired air also contains a variety of particulates that must be properly filtered and/or removed to maintain lung health. Although humans have a certain amount of control over breathing, most functions, including the fine adjustments necessary for proper lung function, are accomplished independent of voluntary control. The goal of this section is to review basic concepts that underlie important aspects of the control and outcome of breathing and introduce other important functions of the lung.

The respiratory system is connected to the outside world by the upper airway that leads down a set of conduits before reaching the gas-exchanging areas (the alveoli). The function of the lungs is supported by a variety of anatomic features that serve to inflate/deflate the lung, thereby allowing the movement of gases to and from the rest of the body. Supporting features include the chest wall, the respiratory muscles, the areas in the brain that control the muscles, and the tracts and nerves that connect the brain to the muscles. The lung also supports the pulmonary circulation, which allows for movement of gases to other organs and tissues of the body. In the first chapter of this section, the unique anatomic and cellular makeup of the respiratory system and how the intricate structure of the lung contributes to respiratory physiology will be explored.

The discussion will continue with an overview of the primary function of the respiratory system—the capture of O2 from the outside environment and its delivery to tissues, as well as the simultaneous removal of CO2 from the tissues to the outside environment. During this discussion, the critical role of pH in gas exchange as well as the ability of the lung to contribute to pH regulation of the blood is examined.

The final chapter in this section begins with an overview of some of the key factors that aid in the control of breathing. This will include the repetitive neuronal firing that controls muscle movements that inflate/deflate the lung and the series of feedback loops that increase/decrease deflation depending on the gas content of the blood. Specific examples of common respiratory abnormalities and how they relate to altered regulation of breathing are also discussed to better understand the intricate feedback loops that help regulate breathing.

Due to the complexity of the lung there is a wide-ranging list of diseases that impact its function. ...

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