OUTLINE 25.1 General Organization and Functions of the Respiratory System 748 25.1a Respiratory System Functions 748 25 25.2 Upper Respiratory Tract 750 25.2a Nose and Nasal Cavity 750 25.2b Paranasal Sinuses 750 25.2c Pharynx 750 25.3 Lower Respiratory Tract 753 Respiratory 25.3a Larynx 753 25.3b Trachea 757 25.3c Bronchial Tree 758 25.3d Respiratory Bronchioles, Alveolar Ducts, and Alveoli 760 System 25.4 Lungs 762 25.4a Pleura and Pleural Cavities 762 25.4b Gross Anatomy of the Lungs 762 25.4c Blood Supply To and From the Lungs 763 25.4d Lymphatic Drainage 765 25.5 Pulmonary Ventilation 766 25.6 Thoracic Wall Dimensional Changes During External Respiration 767 25.7 Innervation of the Respiratory System 769 25.7a Ventilation Control by Respiratory Centers of the Brain 770 25.8 Aging and the Respiratory System 771 25.9 Development of the Respiratory System 774 MODULE 11: RESPIRATORY SYSTEM mck78097_ch25_747-778.indd 747 2/14/11 4:36 PM 748 Chapter Twenty-Five Respiratory System he respiratory (res pi-r ́ ă-tō r ē ́ ; respiro = to breathe) system T provides the means for gas exchange required by living cells. Oxygen must be supplied without interruption, and carbon dioxide, a waste product generated by the cells, must be continuously expelled. Sphenoidal sinus The respiratory and cardiovascular systems are inseparable partners. Frontal sinus While the respiratory system exchanges gases between the atmo- Nasal cavity sphere and the blood, the cardiovascular system transports those Upper gases between the lungs and the body cells. This chapter examines respiratory the cells, tissues, and organs involved in the complex and vital tract Pharynx process of respiration. Larynx 25.1 General Organization and Trachea Functions of the Respiratory System Lower Learning Objectives: respiratory tract Bronchi 1. Identify the components of the conducting and respiratory Lungs portions of the respiratory system. 2. Describe and compare external and internal respiration. 3. Identify and describe the other functions of the respiratory Pleura system. Anatomically, the respiratory system consists of an upper Diaphragm respiratory tract and a lower respiratory tract (figure 25.1). Functionally, it can be divided into a conducting portion, which transports air, and a respiratory portion, where gas exchange with the blood occurs. The conducting portion includes the nose, Figure 25.1 nasal cavity, and pharynx of the upper respiratory tract and the Gross Anatomy of the Respiratory System. The major components larynx, trachea, and progressively smaller airways (from the pri- of the respiratory system are organized into the upper and lower mary bronchi to the terminal bronchioles) of the lower respiratory respiratory tracts. tract. The respiratory portion is composed of small airways called respiratory bronchioles and alveolar ducts as well as air sacs called alveoli in the lower respiratory tract. 25.1a Respiratory System Functions In addition to gas exchange, the respiratory system also func- The primary function most of us associate with the respiratory tions in gas conditioning, sound production, olfaction, and defense. system is breathing, also termed pulmonary ventilation. Breathing consists of two cyclic phases: inhalation (in-hă-lā sh ́ ŭn), also Gas Conditioning called inspiration, and exhalation, also called expiration (eks-pi- As inhaled gases pass through conducting airways, the gases are rā sh ́ ŭ n). Inhalation draws gases into the lungs, and exhalation “conditioned” prior to reaching the gas exchange surfaces of the forces gases out of the lungs. lungs. Specifically, the gases are warmed to body temperature, humidified (moistened), and cleansed of particulate matter through Gas Exchange contact with the respiratory epithelium and its sticky mucous cov- The continuous movement of gases into and out of the lungs is ering. Conditioning is facilitated by the twisted pathways through necessary for the process of gas exchange. There are two types the nasal cavity and paranasal sinuses, which cause the inhaled of gas exchange: external respiration and internal respiration. air to become very turbulent during inhalation. This swirling External respiration involves the exchange of gases between the of inhaled gases means the air remains in the nasal cavity and atmosphere and the blood. Oxygen in the atmosphere is inhaled paranasal sinuses for a relatively longer time, providing greater into the lungs. It diffuses from the lungs into the blood within the opportunity for conditioning. cardiovascular system at the same time carbon dioxide diffuses from the blood into the lungs in order to be exhaled. Internal Sound Production respiration involves the exchange of gases between the blood and As air is forced out of the lungs and moves through the larynx, the cells of the body. Blood transports oxygen from the lungs to sound may be produced, such as speech or singing. Other ana- the body cells and transports carbon dioxide produced by the body tomic structures aid sound production, including the nasal cavity, cells to the lungs. paranasal sinuses, teeth, lips, and tongue. mck78097_ch25_747-778.indd 748 2/14/11 4:36 PM Chapter Twenty-Five Respiratory System 749 Olfaction columnar epithelium lining much of the upper respiratory tract. The superior region of the nasal cavity is covered with olfac- Mucous glands housed within the lamina propria deep to the epi- tory epithelium, which contains receptors for the sense of smell thelium contribute to the layer of mucus covering the epithelium (see chapter 19). These receptors are stimulated when airborne and keep it from drying out. Mucous glands also secrete lysozyme, molecules are inhaled and dissolved in the mucus covering this an enzyme that helps defend against inhaled bacteria. The layer olfactory epithelium. of sticky mucus traps inhaled dust, dirt particles, microorganisms, and pollen. If we are exposed to airborne allergens, large quanti- Defense ties of small particulate material, irritating gases, or pathogens, the Finally, both the structure of the respiratory system and some of rate of mucin production increases. the cells within the respiratory epithelium protect the body against infection by airborne molecules. The entrance to the respiratory WHATW DID YOU LEARN? system (the nose) is inferiorly directed, is lined with coarse hairs, and has twisted passageways to prevent large particles, micro- ●1 Explain the functions carried out by the respiratory system in addition to gas exchange. organisms, and insects from entering. Additionally, numerous goblet cells are dispersed throughout the pseudostratified ciliated ●2 How does mucus help with respiratory system functions? CLINICAL VIEW pulmonary infections are required chronically, because prevention Cystic Fibrosis and early treatment of infection are vital to reducing long-term Cystic fibrosis (sis tiḱ f ¯-broı ¯ sis) ́ is the most common serious genetic complications. Absorption problems caused by pancreatic damage disease in Caucasians, occurring with a frequency of 1 in 3200 births. are treated with orally administered digestive enzymes, vitamins, The condition is inherited as an autosomal recessive trait, and is rare and caloric supplements. Since the gene responsible for cystic among people of Asian and African descent. The name cystic fibrosis fibrosis has been identified, scientists have been investigating refers to the characteristic scarring and cyst formation within the pan- ways to insert copies of the healthy gene into the epithelial cells creas, first recognized in the 1930s. Cystic fibrosis affects the organs of the respiratory tracts of cystic fibrosis patients. In the most that secrete mucin, tears, sweat, digestive juices, and saliva. A defec- promising method found thus far, the healthy gene is transmitted tive gene produces an abnormal plasma membrane protein involved in via a modified adenovirus. chloride ion transport, so individuals with cystic f ibrosis cannot secrete chloride. This lack of chloride secretion causes sodium and water to Mucus builds up and move from the mucus back into the secretory cell itself, thus dehydrat- blocks the bronchial ing the mucus covering the epithelial surface. The mucus becomes thick tree, leading to chronic and sticky, obstructing the airways of the lungs and the ducts of the respiratory infections. pancreas and salivary glands. In the lungs, the mucus becomes so thick it results in airway obstruction. Pulmonary infections, secondary to airway obstruction, are common and can be life-threatening. In the case of the pancreas, the obstructed ducts lead to a backup of digestive enzymes that eventually destroy the pancreas itself. Interestingly, the normal chloride transport protein works in the opposite direction in the sweat glands of the skin. Chloride and sodium are not reabsorbed from the sweat, and so they become concentrated on the skin in individuals with cystic fibrosis. Mothers of babies with Mucus buildup blocks cystic fibrosis often find that the baby tastes “salty” when kissed. the pancreatic ducts and prevents digestive Thus, clinically elevated chloride levels in sweat are one method of enzymes from entering diagnosing the disease. the small intestine. The primary treatment for cystic fibrosis involves agents that Cystic fibrosis results in thickened mucus that obstructs both the break up the thick mucus in the lungs. In addition, antibiotics for respiratory passageways and ducts of glands such as the pancreatic ducts. mck78097_ch25_747-778.indd 749 2/14/11 4:36 PM 750 Chapter