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Pulmonary+Physiology.pdf 1 Pulmonary Physiology, 7th Edition Preface The seventh edition of Pulmonary Physiology has been thoroughly updated. New figures have been added to help students visualize concepts more clearly and learn the material more effectively. New references have been added to the end of each chapter. It has been more than 25 years since Pulmonary Physiology was first published. The book is now older than many of the students reading it! Perhaps the greatest pleasure associated with the first six editions has been receiving the many favorable comments and suggestions made by students, readers, and colleagues, and I have used many of these suggestions in the preparation of this new edition. This book is intended to be used both as an introductory text for beginning students and as a review for residents and fellows in such fields as internal medicine, anesthesiology, pediatrics, and pulmonary medicine. Students who have studied the text should be able to review for licensure and certification examinations by concentrating on the figures, key concepts, tables, and appendices, which summarize nearly all of the material in the book. My goal in writing this book is to provide first-year medical students (as well as respiratory therapy, nursing, nurse-anesthesia, and other students) with a solid background in the aspects of pulmonary physiology essential for an understanding of clinical medicine. My approach is to encourage self-sufficiency not only in studying pulmonary physiology for the first time but also in understanding the basic concepts of pulmonary physiology well enough to apply them with confidence to future patients. I believe that the ways to accomplish this are to inform the reader of the goals of each chapter with clearly stated learning objectives, to give detailed and complete explanations of physiologic mechanisms and demonstrate how they apply to pathologic states, and to give the reader a means of self-testing by providing clinical problems and pulmonary function test data to interpret. The challenge is to write a book that students can read without difficulty in the limited amount of time allocated to pulmonary physiology in the typical curriculum. The material must be presented in a way that discourages memorization without real comprehension, because only those students who understand the basic mechanisms are able to apply them to new situations. The result of this approach should be a book that covers the essentials of the respiratory system as concisely as possible yet raises no questions in students' minds without answering them. I hope that I have achieved these goals in writing this book. I would like to thank the many people whose comments have helped me revise the various editions of the book including my colleagues in respiratory physiology and pulmonary medicine, my colleagues at LSU Health Sciences Center and Tulane University School of Medicine, as well as my students and readers. For this edition I give special thanks to Drs. Andy Pellett of Louisiana State University Health Sciences Center and C. William Davis of the University of North Carolina 2 at Chapel Hill School of Medicine. I would also like to thank everyone who has helped me prepare the manuscripts, illustrations, and proofs including my many editors at McGraw-Hill. For this edition, I would especially like to thank Betsy Giaimo, and my wife Elizabeth. Finally, very special thanks to Gail and Jim Miller of Baton Rouge, Louisiana for taking us in after Hurricane Katrina and making us feel at home for eight months. This book is dedicated to Robert S. Alexander. Michael G. Levitzky Chapter 1. Function & Structure of the Respiratory System OBJECTIVES 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. 3 INTRODUCTION Most of the tissues of the body require oxygen to produce energy, so a continuous supply of oxygen must be available for their normal functioning. Carbon dioxide is a by-product of this aerobic metabolism, and it must be removed from the vicinity of the metabolizing cells. The 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. FUNCTIONS OF THE RESPIRATORY SYSTEM The functions of the respiratory system include gas exchange, acid-base balance, phonation, pulmonary defense and metabolism, and the handling of bioactive materials. Gas Exchange The exchange of carbon dioxide for oxygen takes place in the lungs. Fresh air, containing oxygen, is inspired into the lungs through the conducting airways. The forces needed to cause 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. 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 4 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. Other Functions ACID-BASE BALANCE In the body, increases in carbon dioxide lead to increases in hydrogen ion concentration (and vice versa) because of the following reaction: 5 The respiratory system can therefore participate in acid-base balance by removing CO2 from the body. The central nervous system has sensors for the CO2 and the hydrogen ion levels in the arterial blood and in the cerebrospinal fluid that send information to the controllers of breathing. Acid-base balance is discussed in greater detail in Chapter 8; the control of breathing is discussed in Chapter 9. PHONATION Phonation is the production of sounds by the movement of air through the vocal cords. Speech, singing, and other sounds are produced by the actions of the central nervous system controllers on the muscles of respiration, causing air to flow through the vocal cords and the mouth. Phonation will not be discussed in detail in this book. PULMONARY DEFENSE MECHANISMS Each breath brings into the lungs a small sample of the local atmospheric environment. This may include microorganisms such as bacteria, dust, particles of silica or asbestos, toxic gases, smoke (cigarette and other types), and other pollutants. In addition, the temperature and humidity of the local atmosphere vary tremendously. The mechanisms by which the lungs are protected from these environmental assaults are discussed in Chapter 10. PULMONARY METABOLISM AND THE HANDLING OF BIOACTIVE MATERIALS The cells of the lung must metabolize substrates to supply energy and nutrients for their own maintenance. Some specialized pulmonary cells also produce substances necessary for normal pulmonary function. In addition, the pulmonary capillary endothelium contains a great number of enzymes that can produce, metabolize, or modify naturally occurring vasoactive substances. These metabolic functions of the respiratory system are discussed in Chapter 10. STRUCTURE OF THE RESPIRATORY SYSTEM Air enters the respiratory system through the nose or mouth. Air entering through the nose is filtered, heated to body temperature, and humidified as it passes through the ...