Rosen Educational Services materials copyright 2011 Rosen Educational Services, LLC. All rights reserved.

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2 Published in 2011 by Britannica Educational Publishing (a trademark of Encyclopædia Britannica, Inc.) in association with Rosen Educational Services, LLC 29 East 21st Street, New York, NY Copyright 2011 Encyclopædia Britannica, Inc. Britannica, Encyclopædia Britannica, and the Thistle logo are registered trademarks of Encyclopædia Britannica, Inc. All rights reserved. Rosen Educational Services materials copyright 2011 Rosen Educational Services, LLC. All rights reserved. Distributed exclusively by Rosen Educational Services. For a listing of additional Britannica Educational Publishing titles, call toll free (800) First Edition Britannica Educational Publishing Michael I. Levy: Executive Editor J.E. Luebering: Senior Manager Marilyn L. Barton: Senior Coordinator, Production Control Steven Bosco: Director, Editorial Technologies Lisa S. Braucher: Senior Producer and Data Editor Yvette Charboneau: Senior Copy Editor Kathy Nakamura: Manager, Media Acquisition Kara Rogers: Senior Editor, Biomedical Sciences Rosen Educational Services Heather M. Moore Niver: Editor Nelson Sá: Art Director Cindy Reiman: Photography Manager Matthew Cauli: Designer, Cover Design Introduction by Amy Miller Library of Congress Cataloging-in-Publication Data The respiratory system / edited by Kara Rogers. p. cm. -- (The human body) In association with Britannica Educational Publishing, Rosen Educational Services. Includes bibliographical references and index. ISBN (library binding) 1. Respiratory organs Popular works. I. Rogers, Kara. QP121.R dc Manufactured in the United States of America On the cover: The human lungs are extraordinary organs that constantly pump crucial oxygen through airways and into the bloodstream. / Sebastian Kaulitzki On page 10: Singing is one of many common activities that requires dynamic breath control. Chip Somodevilla/Getty Images On pages 19, 41, 60, 87, 122, 159, 196, 226, 228, 230: A healthy set of lungs is the powerhouse behind the respiratory system. / nicoolay

3 CONTENTS Introduction 10 Chapter 1: Anatomy and Function of the Human Respiratory System 19 The Design of the Respiratory System 19 Morphology of the Upper Airways 21 The Nose 21 The Pharynx 24 Morphology of the Lower Airways 25 The Larynx 26 The Trachea and the Stem Bronchi 28 Structural Design of the Airway Tree 29 The Lungs 31 Gross Anatomy 31 Pulmonary Segments 33 The Bronchi and Bronchioles 33 The Gas-Exchange Region 34 Blood Vessels, Lymphatic Vessels, and Nerves 36 Lung Development 38 Chapter 2: Control and Mechanics of Breathing 41 Control of Breathing 41 Central Organization of Respiratory Neurons 44 Chemoreceptors 46 Peripheral Chemoreceptors 46 Central Chemoreceptors 48 Muscle and Lung Receptors 49 Variations in Breathing 50 Exercise 51 Sleep

4 61 The Mechanics of Breathing 53 The Lung Chest System 55 The Role of Muscles 56 The Respiratory Pump and Its Performance 57 Chapter 3: Gas Exchange and Respiratory Adaptation 60 Gas Exchange 60 Transport of Oxygen 63 Transport of Carbon Dioxide 65 Gas Exchange in the Lung 68 Abnormal Gas Exchange 69 Interplay of Respiration, Circulation, and Metabolism 73 Adaptations 78 High Altitudes 79 Swimming and Diving Chapter 4: Infectious Diseases of the Respiratory System 87 Upper Respiratory System Infections 88 Common Cold 88 Sore Throat 91 Pharyngitis 91 Sinusitis 92 Tonsillitis 94 Lower Respiratory System Infections 95 Laryngitis 95 Tracheitis 96 Croup 98 Infectious Bronchitis 99 Bronchiolitis 100 Influenza 102 Whooping Cough 105

5 Psittacosis 107 Pneumonia 108 Legionnaire Disease 113 Tuberculosis 114 Chapter 5: Diseases and Disorders of the Respiratory System 122 Disorders of the Upper Airway 122 Snoring 123 Sleep Apnea 124 Pickwickian Syndrome 126 Diseases of the Pleura 126 Pleurisy 127 Pleural Effusion and Thoracic Empyema 127 Pneumothorax 129 Diseases of the Bronchi and Lungs 130 Bronchiectasis 130 Chronic Bronchitis 131 Pulmonary Emphysema 133 Chronic Obstructive Pulmonary Disease 136 Lung Congestion 138 Atelectasis 141 Lung Infarction 144 Cystic Fibrosis 145 Idiopathic Pulmonary Fibrosis 149 Sarcoidosis and Eosinophilic Granuloma 149 Pulmonary Alveolar Proteinosis 150 Immunologic Conditions of the Lung 151 Lung Cancer 152 Diseases of the Mediastinum and Diaphragm

6 Chapter 6: Allergic and Occupational Lung Diseases and Acute Respiratory Conditions 159 Allergic Lung Diseases 159 Asthma 160 Hay Fever 164 Hypersensitivity Pneumonitis 166 Occupational Lung Disease 167 Silicosis 169 Black Lung 170 Asbestosis and Mesothelioma 171 Respiratory Toxicity of Glass and Metal Fibres 173 Byssinosis 174 Respiratory Toxicity of Industrial Chemicals 175 Disability and Attribution of Occupational Lung Diseases 176 Other Respiratory Conditions 177 Circulatory Disorders 177 Respiratory Distress Syndrome 179 Air Pollution 180 Carbon Monoxide Poisoning 183 Acidosis 184 Alkalosis and Hyperventilation 184 Hypoxia 186 Altitude Sickness 188 Barotrauma and Decompression Sickness 189 Thoracic Squeeze 192 Drowning 193 Chapter 7: Approaches to Respiratory Evaluation and Treatment 196 Recognizing the Signs and Symptoms of Disease 196

7 Methods of Investigation 199 Pulmonary Function Test 202 Chest X-ray 203 Lung Ventilation/Perfusion Scan 204 Bronchoscopy 205 Mediastinoscopy 208 Types of Respiratory Therapy 210 Drug Therapies 211 Oxygen Therapy 214 Artificial Respiration 218 Thoracentesis 220 Hyperbaric Chamber 221 Lung Transplantation 223 Conclusion 223 Glossary 226 Bibliography 228 Index

8 INTRODUCTION

9 7 Introduction 7 The human lungs are amazing feats of nature. They pump vital oxygen through airways and into the bloodstream every second of every day. Without this ability, humans could not survive on Earth. This book explains the science behind the amazing human respiratory system. It also sheds light on how easily a healthy respiratory system can be damaged, whether by a viral or bacterial infection or through detrimental habits such as smoking. But there are many treatments to keep the airways free and clear, and this book also describes the many different approaches doctors can take to save patients lives and lungs. The anatomy of the human respiratory system starts at the place where air first enters the body the nose. This structure provides humans with the sense of smell while also filtering, warming, and moistening inhaled air. Air that passes through the nose travels to the pharynx, or throat, the cone-shaped passageway leading from the mouth and nose to the larynx, or voice box. The larynx is a hollow tube connected to the top of the windpipe, and this air canal to the lungs not only enables humans to speak but also keeps food out of the lower respiratory tract. After passing through the larynx, air travels through the trachea, also known as the windpipe. Here, the air is cleansed and moistened before entering the lungs. The clean air then travels into the deep tissues of the lungs, eventually reaching the region where gas is exchanged, the centre of the respiratory system. The right lung is slightly larger than the left lung because of the asymmetrical position of the heart. The right lung has 10 airway segments, and the left lung has 8 to 10. A thin membranous sac known as the pleura covers the lungs. Inside the lungs, there are numerous nerves and blood vessels. However, the most prominent feature of the lung interior are the many small air passages called 11

10 7 The Respiratory System 7 bronchioles, which range in diameter from 3 mm (0.12 inch) to less than 1 mm (less than 0.04 inch). The gas-exchange area, the region where oxygen is transferred to the blood and carbon dioxide is removed, is made up of three separate compartments for blood, air, and tissue. The tissue compartment supports the air and blood compartments and lets them come into close contact, which makes exchanging gases easier, but still keeps them separate. The exchange of carbon dioxide and oxygen takes place in tiny air sacs called alveoli, which look like cells in a honeycomb. The average adult lung has approximately 300 million alveoli. Lungs also have two distinct blood circulation systems. The first of these, the pulmonary system, is characterized by the transport of carbon dioxide laden blood from the right side of the heart, through the pulmonary arteries, and to the lungs and by the subsequent transport of oxygen-rich blood from the lungs, through the pulmonary veins, and to the left atrium of the heart. From the heart, the oxygenated blood is pumped to the rest of the body, thereby delivering oxygen and other nutrients to organs distant from the lungs. The second blood system in the lungs, the bronchial circulation, comprises the network of blood vessels supporting the conducting airways themselves. The bronchial circulation is a vital source of nourishment for the lung tissues. The act of breathing, or respiration, is an automatic process, controlled by the brain. Thus, humans and other animals do not need to actively think about breathing in order for it to happen. A significant feature of the human respiratory system is its capacity to instantly adjust to internal and external stimuli on its own. A series of neural networks in the brain control the rate of breathing by communicating with the muscles in the chest and the 12

11 7 Introduction 7 abdomen. One of the major abdominal muscles involved in breathing is the diaphragm, which functions to move air in and out of the lungs as it contracts and relaxes, respectively. The neural networks controlling breathing receive information from special chemical sensors known as chemoreceptors, which are located throughout the body. Whereas some chemoreceptors respond to changes in oxygen and carbon dioxide levels in the bloodstream, others respond to chemical changes in the immediate external environment. Some chemoreceptors send signals to the brain when they detect noxious or toxic materials in air as it passes to the lungs. When stimulated, these receptors constrict the airways and cause breathing to become fast and shallow. This response represents the body s attempt to prevent toxins from entering the lungs. In addition to the types of sensors described above, there also exist sensors that monitor the muscles that control breathing. One of the most notable features of respiratory control is the way in which neural communication between the body and the brain fine-tunes the rate of breathing in order to keep carbon dioxide pressure in the blood constant. This fine level of regulation is fundamental in maintaining the acid base balance in the body. The effects of this are illustrated by the differences in respiration rate observed during exercise and during sleep. During exercise, metabolic rate and acid levels in muscle tissue increase. These effects trigger an increase in respiration rate, thereby increasing oxygen delivery to tissues and maintaining the body s acid base balance. In contrast, during sleep, metabolic rate slows and therefore respiration rate decreases and oxygen demand is low. In the basic mechanics of breathing, air moves in and out of the lungs in response to pressure changes. The 13

12 7 The Respiratory System 7 diaphragm is the major muscle that facilitates breathing, but it is assisted by a complex assembly of other muscle groups. The amount of air that the lungs pump changes dramatically depending on external or internal conditions. In adults, during vigorous breathing, the volume of air expired by the lungs can increase by as much as 25 times the normal resting level. The lungs serve a fundamental role in ensuring that excess carbon dioxide is removed from the body. The pulmonary alveoli, the small air spaces in the lungs, transfer carbon dioxide from and add oxygen to blood. This exchange of gases takes place over an immense surface area. The carbon dioxide that is absorbed by the alveoli is expelled from the body during exhalation. The oxygen that the alveoli transfer to the blood is then circulated to the heart and the body s other tissues. Respiration, circulation, and metabolism all work together. The main purpose of respiration is to provide oxygen for the body s cells. Oxygen is used by cells for the breakdown of nutrients, an activity that is necessary to supply energy to the cells and the body. Without oxygen, cells are unable to function properly. Oxygen deprivation, even for only a few minutes, can cause the brain and the heart to stop functioning, which can lead to death. The atmospheric pressure of oxygen differs with respect to high versus low altitudes on Earth. At high altitudes, oxygen is present at lower levels than it is at low altitudes. People who live at high altitudes adapt to this decrease in oxygen availability. However, acclimatization, in which the body works to more efficiently utilize oxygen in the air, is a gradual process. Mountain climbers ascending to extreme heights must spend several days at camps established increasingly farther up the mountainside, hiking up during the day and descending down to camp to 14

13 7 Introduction 7 sleep at night. This enables the body to adjust to the decreased availability of oxygen. If these precautions are not taken, as climbers make their way up the mountain, the body s tissues become deprived of oxygen, which can lead to high-altitude pulmonary edema, in which the body circulates additional blood to the lungs, but the blood leaks into the air sacs. Essentially, death is caused by drowning. Various infectious diseases caused by viruses and bacteria can produce difficulties in breathing. The common cold is an acute infection of the upper respiratory tract that can sometimes spread to the lower respiratory tissues. Other common upper respiratory conditions include sore throat and pharyngitis, which can arise as a result of infection. Inflammation of respiratory tissues can sometimes be severe and chronic. For example, many people have their tonsils removed after suffering from chronic tonsillitis. In the lower respiratory system, bacteria can cause inflammation of the trachea, a condition known as tracheitis, as well as bacterial pneumonia, which can be particularly dangerous in infants and in the elderly. Before antibiotics were widely available, pneumonia was a widespread and notoriously deadly disease. Although bacteria sometimes cause pneumonia, certain viruses and fungi can also cause the disease. Pneumonia also often affects persons with impaired immune systems, because these individuals are unable to defend against infectious organisms. Tuberculosis is another example of a respiratory disease caused by bacteria. In the 18th and 19th centuries, it was a leading cause of death, and in the first decade of the 21st century, the emergence of drug-resistant tuberculosis bacteria has resulted in a resurgence of the disease. The 15

14 7 The Respiratory System 7 tuberculosis bacteria spread slowly in the lungs and cause hard nodules (tubercles), or large cheese-like masses, to form. This process leads to the eventual breakdown of respiratory tissues, resulting in the formation of cavities in the lungs. Eventually, blood vessels in the lungs burst, and the infected person coughs up bright red blood. Influenza is a common, seasonal respiratory illness that is caused by viral infection. Infection is accompanied by fever, chills, muscle pains, headaches, and stomach pain. It is a highly contagious disease too. Every few decades, a strain of influenza virus gives rise to a pandemic, an outbreak of the illness that occurs on a global scale and is characterized by rapid spread. One of the deadliest influenza pandemics was that of , which caused between 25 million and 50 million deaths worldwide. Many respiratory conditions arise from noninfectious causes. For example, snoring is caused by blocked airways, which may be associated with obesity. A severe form of snoring is sleep apnea, in which the collapse of the airways leads to intermittent stoppages in breathing. Sleep apnea causes affected individuals to awaken periodically through the night. Some respiratory diseases are inherited. One of the best-characterized inherited conditions is cystic fibrosis, the primary symptom of which is the production of a thick, sticky mucus that blocks the airways and the digestive tract. For some diseases of the respiratory system, no cause has been identified, despite extensive research. One example is idiopathic pulmonary fibrosis, which results in progressive shortness of breath until a person can no longer breathe. The term idiopathic means of unknown cause, and thus is used to describe diseases of uncertain origin. A respiratory disease of major concern in the world today is lung cancer. Lung cancer can arise as a result of a 16