Essentials of Human Anatomy & Physiology (Chapter 13) PDF

M13_MARI6119_12_GE_C13.indd Page 462 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO....

M13_MARI6119_12_GE_C13.indd Page 462 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 13 The Respiratory System WHAT The respiratory system provides oxygen HOW to the body, disposes of carbon dioxide, and helps reguate Gas exchange blood pH. occurs in the air sacs of the lungs, called alveoli, and at capillary beds around the body. WHY Without oxygen, cells will eventually die. Too much carbon dioxide in the blood will cause the blood pH Instructors to become acidic, which will New Building Vocabulary interfere with cellular Coaching Activities for this function. chapter are assignable in Copyright © 2017. Pearson Education Limited. All rights reserved. T he trillions of cells in the body require an abundant and endless supply of oxygen to carry out their vital functions. We cannot “do without” oxygen for even a little while, as we can without food or water. Furthermore, as cells transport respiratory gases between the lungs and the cells in the rest of the body. If either system fails, cells begin to die from oxygen starvation and accumulation of carbon dioxide. use oxygen, they give off carbon dioxide, a waste product the body must get rid of. Functional Anatomy The cardiovascular and respiratory systems of the Respiratory System share responsibility for supplying the body with oxygen and disposing of carbon dioxide. The ➔ Learning Objectives respiratory system organs oversee the gas □□ Name the organs forming the respiratory exchanges that occur between the blood and the passageway from the nasal cavity to the alveoli of the lungs (or identify them on a diagram or model), external environment. Using blood as the trans- and describe the function of each. porting fluid, the cardiovascular system organs □□ Describe several protective mechanisms of the respiratory system. 462 Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 463 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 463 Nasal cavity Oral cavity Nostril Pharynx Larynx Trachea Left main Right main (primary) (primary) bronchus bronchus Left lung Right lung Diaphragm Figure 13.1 The major respiratory organs shown in relation to surrounding structures. The organs of the respiratory system include the system. During breathing, air enters the nose by nose, pharynx, larynx, trachea, bronchi and their passing through the nostrils, or nares. The inte- smaller branches, and the lungs, which contain the rior of the nose consists of the nasal cavity, Copyright © 2017. Pearson Education Limited. All rights reserved. alveoli (al-ve′o-li), or terminal air sacs (Figure 13.1). divided by a midline nasal septum. The olfactory Because gas exchange with the blood happens receptors for the sense of smell are located in the only in the alveoli, the other respiratory system mucosa in the slitlike superior part of the nasal structures are really just conducting passageways cavity, just beneath the ethmoid bone. ➔ that carry air through the lungs. The passageways from the nose to the larynx are called the upper ConceptLink respiratory tract, and those from the trachea to the Recall that any area open to the outside of the body, alveoli are the lower respiratory tract. These con- including respiratory passages, is lined with mucous ducting passageways also purify, humidify, and membrane (mucosa), which is a “wet,” or moist, mem- 13 warm incoming air. Thus, the air finally reaching brane (Chapter 4, p. 136). the lungs has fewer irritants (such as dust or bacte- ria) than the air outside, and it is warm and damp. The rest of the mucosa lining the nasal cavity, called the respiratory mucosa, rests on a rich net- The Nose work of thin-walled veins that warms the air as it The nose, whether “button” or “hooked” in shape, flows past. In addition, the sticky mucus produced is the only externally visible part of the respiratory by this mucosa’s glands moistens the air and traps Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 464 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 464 Essentials of Human Anatomy and Physiology incoming bacteria and other foreign debris, and and postnasal drip. Because the nasal mucosa is lysozyme enzymes in the mucus destroy bacteria continuous throughout the respiratory tract and chemically. The ciliated cells of the nasal mucosa extends tentacle-like into the nasolacrimal (tear) create a gentle current that moves the sheet of ducts and paranasal sinuses, nasal cavity infections contaminated mucus posteriorly toward the throat often spread to those regions as well. Sinusitis, or (pharynx), where it is swallowed and digested by sinus inflammation, is difficult to treat and can stomach juices. We are usually unaware of this cause marked changes in voice quality. When the important ciliary action, but when the external passageways connecting the sinuses to the nasal temperature is extremely cold, these cilia become cavity are blocked with mucus or infectious matter, sluggish, allowing mucus to accumulate in the the air in the sinus cavities is absorbed. The result is nasal cavity and to dribble outward through the a partial vacuum and a sinus headache localized nostrils. This helps explain why you might have a over the inflamed area. ________________________ ✚ “runny” nose on a crisp, wintry day. The lateral walls of the nasal cavity are uneven, The Pharynx owing to three mucosa-covered projections, or The pharynx (far′inks) is a muscular passageway lobes, called conchae (kong′ke). The conchae about 13 cm (5 inches) long that vaguely resem- greatly increase the surface area of the mucosa bles a short length of red garden hose. Commonly exposed to the air (as shown in Figure 13.2). The called the throat, the pharynx serves as a common conchae also increase the air turbulence in the passageway for food and air (see Figure 13.2). It is nasal cavity. As the air swirls through the twists continuous with the nasal cavity anteriorly via the and turns, inhaled particles are deflected onto the posterior nasal aperture. mucus-coated surfaces, where they are trapped The pharynx has three regions (Figure 13.2a). Air and prevented from reaching the lungs. enters the superior portion, the nasopharynx The nasal cavity is separated from the oral cav- (na″zo-far′inks), from the nasal cavity and then ity below by a partition, the palate (pal′et). descends through the oropharynx (o″ro-far′inks) Anteriorly, where the palate is supported by bone, and laryngopharynx (lah-ring″go-far′inks) to enter is the hard palate; the unsupported posterior the larynx below. Food enters the mouth, then trav- part is the soft palate. els along with air through the oropharynx and laryn- gopharynx. But instead of entering the larynx, food Homeostatic Imbalance 13.1 is directed into the esophagus (ĕ-sof′ah-gus) posteri- orly by a flap called the epiglottis (ep″ı̆-glot′is). The genetic defect cleft palate (failure of the bones The pharyngotympanic tubes, which drain the forming the palate to fuse medially) results in breath- middle ears, open into the nasopharynx. The muco- ing difficulty as well as problems with oral cavity sae of these two regions are continuous, so ear functions, such as nursing and speaking. _________✚ infections such as otitis media (o-ti′tis me′de-ah) Copyright © 2017. Pearson Education Limited. All rights reserved. may follow a sore throat or other types of pharyn- The nasal cavity is surrounded by a ring of para- geal infections. nasal sinuses located in the frontal, sphenoid, eth- Clusters of lymphatic tissue called tonsils are moid, and maxillary bones. (See Figure 5.13, p. 177.) also found in the pharynx. The single pharyngeal The sinuses lighten the skull and act as resonance (far-rin′je-al) tonsil, often called the adenoid, is chambers for speech. They also produce mucus, located high in the nasopharynx. The two pala- which drains into the nasal cavities. The suctioning tine tonsils are in the oropharynx at the end of effect created by nose blowing helps to drain the the soft palate, as are the two lingual tonsils, sinuses. The nasolacrimal ducts, which drain tears which lie at the base of the tongue. The tonsils from the eyes, also empty into the nasal cavities. also play a role in protecting the body from infec- tion (see Chapter 12). Homeostatic Imbalance 13.2 Cold viruses and various allergens can cause rhinitis Homeostatic Imbalance 13.3 (ri-ni′tis), inflammation of the nasal mucosa. The If the pharyngeal tonsil becomes inflamed and excessive mucus produced results in nasal congestion swollen (as during a bacterial infection), it obstructs Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 465 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 465 Figure 13.2 Basic anatomy of the upper respiratory tract, sagittal section. Pharynx Nasopharynx Oropharynx Laryngopharynx (a) Regions of the pharynx Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Posterior nasal Nasal cavity aperture Nasal conchae (superior, middle, and inferior) Nasopharynx Pharyngeal tonsil Nasal meatuses (superior, Opening of middle, and inferior) pharyngotympanic tube Nasal vestibule Uvula Nostril Oropharynx Hard palate Palatine tonsil Soft palate Lingual tonsil Tongue Laryngopharynx Hyoid bone Copyright © 2017. Pearson Education Limited. All rights reserved. Larynx Esophagus Epiglottis Thyroid cartilage Trachea Vocal fold Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract 13 the nasopharynx and forces the person to breathe they were routinely removed. Now, with the through the mouth. In mouth breathing, air is not widespread use of antibiotics, this is no longer properly moistened, warmed, or filtered before necessary. __________________________________ ✚ reaching the lungs. Many children routinely get this condition, called tonsillitis. Years ago the The Larynx belief was that the tonsils, though protective, The larynx (lar′inks), or voice box, routes air and were more trouble than they were worth, and food into the proper channels and plays a role in Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 466 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 466 Essentials of Human Anatomy and Physiology speech. Located inferior to the pharynx (Figure 13.2b), it is formed by eight rigid hyaline cartilages Homeostatic Imbalance 13.4 and a spoon-shaped flap of elastic cartilage, the Because the trachea is the only way air can enter epiglottis. The largest of the hyaline cartilages is the lungs, tracheal obstruction is life-threatening. the shield-shaped thyroid cartilage, which pro- Many people have suffocated after choking on a trudes anteriorly and is commonly called the piece of food that suddenly closed off the trachea Adam’s apple. (or the glottis of the larynx). The Heimlich Sometimes referred to as the “guardian of the maneuver, a procedure in which the air in a per- airway,” the epiglottis protects the superior open- son’s own lungs is used to “pop out,” or expel, an ing of the larynx. During regular breathing, the obstructing piece of food, has saved many people epiglottis allows the passage of air into the lower from becoming victims of choking. The Heimlich respiratory passages. When we swallow food or maneuver is simple to learn and easy to do. fluids, the situation changes dramatically; the lar- However, it is best learned by demonstration ynx is pulled upward, and the epiglottis tips, form- because cracked ribs are a distinct possibility ing a lid over the larynx’s opening. This routes when it is done incorrectly. In some cases of food into the esophagus, which leads to the stom- obstructed breathing, an emergency tracheostomy ach, posteriorly. If anything other than air enters (tra′ke-ost′o-me; surgical opening of the trachea) the larynx, a cough reflex is triggered to prevent is done to provide an alternative route for air to the substance from continuing into the lungs. reach the lungs. Individuals with tracheostomy tubes Because this protective reflex does not work when in place form huge amounts of mucus the first few we are unconscious, never try to give fluids to an days because of irritation to the trachea. Thus, they unconscious person when attempting to revive must be suctioned frequently during this time to pre- him or her. vent the mucus from pooling in their lungs. _______✚ Palpate your larynx by placing your hand ­midway on the anterior surface of your neck. The trachea is lined with a ciliated mucosa Swallow. Can you feel the larynx rising as you (Figure 13.3b). The cilia beat continuously in a swallow? superior direction. They are surrounded by goblet cells that produce mucus. The cilia propel this Part of the mucous membrane of the larynx mucus, loaded with dust particles and other debris, forms a pair of folds, called the vocal folds, or away from the lungs to the throat, where it can be true vocal cords, which vibrate with expelled air. swallowed or spat out. This ability of the vocal folds to vibrate allows us to speak. The vocal folds and the slitlike passage- way between them are called the glottis. Homeostatic Imbalance 13.5 The Trachea Smoking inhibits and ultimately destroys the cilia. Copyright © 2017. Pearson Education Limited. All rights reserved. Without these cilia, coughing is the only means of Air entering the trachea (tra′ke-ah), or windpipe, preventing mucus from accumulating in the lungs. from the larynx travels down its length (10–12 cm, Smokers with respiratory congestion should avoid or about 4 inches) to the level of the fifth thoracic medications that inhibit the cough reflex. _______✚ vertebra, which is approximately midchest (see Figure 13.1). Did You Get It? The trachea is fairly rigid because its walls are 1. Why is nose breathing preferable to mouth reinforced with C-shaped rings of hyaline carti- breathing? lage (Figure 13.3a). These rings serve a double pur- 2. What is the specific protective function of cilia in the pose. The open parts of the rings abut the esophagus trachea? and allow it to expand anteriorly when we swallow For answers, see Appendix A. a large piece of food. The solid portions support the trachea walls and keep it patent, or open, in spite of The Main Bronchi the pressure changes that occur during breathing. The right and left main (primary) bronchi The trachealis muscle lies next to the esophagus (brong′ki) are formed by the division of the tra- and completes the wall of the trachea posteriorly. chea. Each main bronchus runs obliquely before it Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 467 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 467 Q: In what direction is the power stroke of these cilia directed—superiorly toward the mouth or inferiorly toward the lungs? Posterior Mucosa Esophagus Submucosa Trachealis Lumen of Seromucous muscle trachea gland in submucosa Hyaline cartilage Adventitia Anterior (a) (b) Figure 13.3 Anatomy of the trachea and esophagus. (a) A cross-sectional view of View Histology the structural relationship between the trachea and esophagus. (b) Cilia in the trachea. The cilia are the yellow, grasslike projections surrounded by the mucus-secreting goblet cells, which exhibit short microvilli (orange). (Scanning electron micrograph, 1,800×.) plunges into the medial depression (hilum) of the houses the heart, the great blood vessels, bronchi, lung on its own side (see Figure 13.1). The right the esophagus, and other organs (Figure 13.4, main bronchus is wider, shorter, and straighter p. 468). The narrow superior portion of each lung, than the left. Consequently, it is the more com- the apex, is just deep to the clavicle. The broad mon site for an inhaled foreign object to become lung area resting on the diaphragm is the base. lodged. By the time incoming air reaches the Each lung is divided into lobes by fissures; the left bronchi, it is warm, cleansed of most impurities, lung has two lobes, and the right lung has three. and humid. The smaller subdivisions of the main The surface of each lung is covered with its bronchi within the lungs are direct routes to the own visceral serosa, called the pulmonary pleura Copyright © 2017. Pearson Education Limited. All rights reserved. air sacs. or visceral pleura (ploor′ah), and the walls of the thoracic cavity are lined by the parietal pleura. The Lungs The pleural membranes produce pleural fluid, ➔ Learning Objectives slippery serous fluid, which allows the lungs to □□ Describe the structure and function of the lungs glide easily over the thorax wall during breathing and the pleural coverings. and causes the two pleural layers to cling together. □□ Describe the structure of the respiratory The pleurae can slide easily from side to side membrane. across one another, but they strongly resist being pulled apart. Consequently, the lungs are held 13 The lungs are fairly large organs. They occupy the tightly to the thorax wall, and the pleural space is entire thoracic cavity except for the most central more of a potential space than an actual one. As area, the mediastinum (me″de-as-ti′num), which we describe shortly, this tight adherence of the pleural membranes is absolutely essential for nor- mal breathing. (Figure 13.4a shows the position of A: unwanted substances from entering the lungs. Superiorly toward the mouth, to prevent the pleurae on the lungs and the thorax wall.) Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 468 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 468 Essentials of Human Anatomy and Physiology Figure 13.4 Anatomical relationships of organs in the thoracic cavity. Part (a) includes a close-up illustration of the Intercostal muscle pleurae. In (b), the size of the pleural (and pericardial) cavity is exaggerated for clarity. Rib Parietal pleura Lung Pleural cavity Trachea Visceral pleura Thymus Apex of lung Left superior lobe Right superior lobe Oblique Horizontal fissure fissure Right middle lobe Left inferior lobe Oblique fissure Right inferior lobe Heart (in pericardial cavity of mediastinum) Diaphragm Base of lung (a) Anterior view. The lungs flank mediastinal structures laterally. Posterior Vertebra Esophagus (in posterior mediastinum) Root of lung at hilum Right lung Left main bronchus Copyright © 2017. Pearson Education Limited. All rights reserved. Left pulmonary artery Parietal pleura Left pulmonary vein Visceral pleura Left lung Pleural cavity Thoracic wall Pulmonary trunk Pericardial membranes Heart (in mediastinum) Anterior mediastinum Sternum Anterior (b) Transverse section through the thorax, viewed from above Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 469 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 469 Alveolar duct Alveoli Respiratory bronchioles Alveolar duct Terminal bronchiole Alveolar sac (a) Diagrammatic view of respiratory bronchioles, alveolar ducts, and alveoli Alveolar duct Alveolar pores Alveolus (b) Light micrograph of human lung tissue, showing the final divisions of the respiratory tree (120×) View Histology Figure 13.5 Respiratory zone structures. est of the conducting passageways, the bronchioles Copyright © 2017. Pearson Education Limited. All rights reserved. Homeostatic Imbalance 13.6 (brong′ke-ˉolz). Because of this branching and Pleurisy (ploo′rı̆-se), inflammation of the pleurae, rebranching of the respiratory passageways within can be caused by insufficient secretion of pleural the lungs, the network formed is often referred to as fluid. The pleural surfaces become dry and rough, the bronchial, or respiratory, tree. All but the smallest resulting in friction and stabbing pain with each branches have reinforcing cartilage in their walls. breath. Conversely, the pleurae may produce Respiratory Zone Structures and excessive amounts of fluid, which exerts pressure the Respiratory Membrane on the lungs. This type of pleurisy hinders breath- ing movements, but it is much less painful than The terminal bronchioles lead into respiratory 13 the dry rubbing type. _________________________✚ zone structures, even smaller conduits that eventu- ally terminate in alveoli (al-ve′o-li; alveol = small The Bronchial Tree cavity), or air sacs. The respiratory zone, which After entering the lungs, the main bronchi subdivide includes the respiratory bronchioles, alveolar into smaller and smaller branches (secondary and ter- ducts, alveolar sacs, and alveoli, is the only site of tiary bronchi, and so on), finally ending in the small- gas exchange (Figure 13.5). All other respiratory Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 470 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 470 Essentials of Human Anatomy and Physiology Red blood cell Endothelial cell nucleus Capillary Alveolar pores O2 Capillary CO2 Macrophage Alveolus Nucleus of squamous epithelial cell Respiratory Alveolar epithelium membrane Fused basement membranes Capillary endothelium Alveoli (gas- Red blood Surfactant- Squamous filled air cell in secreting cell epithelial cell spaces) capillary of alveolar wall Figure 13.6 Functional anatomy capillary endothelium, and the scant oxygen diffuses from the alveolar of the respiratory membrane basement membranes between. air across this membrane into the (air-blood barrier). As shown in Surfactant-secreting cells in the pulmonary capillary blood; carbon the left illustration, the respiratory alveoli are also shown. Small pores dioxide diffuses from the pulmonary membrane is composed of squamous connect neighboring alveoli. As blood into the alveolus. epithelial cells of the alveoli, the shown in the right illustration, passages are conducting zone structures that membrane (air-blood barrier) (Figure 13.6). The serve as conduits to and from the respiratory zone. respiratory membrane has gas (air) flowing past on There are millions of the clustered alveoli, which one side and blood flowing past on the other. Gas resemble bunches of grapes, and they make up exchange occurs by simple diffusion through the the bulk of the lungs. Consequently, the lungs are respiratory membrane—oxygen passes from the mostly air spaces. The balance of the lung tissue, alveolar air into the capillary blood, and carbon Copyright © 2017. Pearson Education Limited. All rights reserved. its stroma, is mainly elastic connective tissue that dioxide leaves the blood to enter the alveoli (Figure allows the lungs to stretch and recoil (spring back) 13.6). The total gas exchange surface provided by as we breathe. Thus, in spite of their relatively the alveolar walls of a healthy man is estimated to large size, the lungs weigh only about 2½ pounds, be 50 to 70 square meters, or approximately 40 and they are soft and spongy. times greater than the surface area of his skin! The walls of the alveoli are composed largely The final line of defense for the respiratory of a single, thin layer of simple squamous epithelial system is in the alveoli. Remarkably efficient alve- cells. The thinness of their walls is hard to imagine, olar macrophages, sometimes called “dust cells,” but a sheet of tissue paper is much thicker. Alveolar wander in and out of the alveoli picking up bacte- pores connect neighboring air sacs and provide ria, carbon particles, and other debris. Also scat- alternative routes for air to reach alveoli whose tered amid the epithelial cells that form most of feeder bronchioles have been clogged by mucus or the alveolar walls are cuboidal surfactant-secreting otherwise blocked. The external surfaces of the cells, which look very different from the squamous alveoli are covered with a “cobweb” of pulmonary epithelial cells. These cells produce a lipid (fat) capillaries. Together, the alveolar and capillary molecule called surfactant, which coats the gas- walls, their fused basement membranes, and occa- exposed alveolar surfaces and is very important in sional elastic fibers construct the respiratory lung function (as described on p. 483). Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 471 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 471 Did You Get It? oxygen to produce ATP and carbon dioxide, is the 3. Name the order of the following parts of the human cornerstone of all energy-producing chemical respiratory system from the site where air enters the reactions and occurs in all cells (see Chapter 14). nostrils to the site where air reaches the end passages of the lungs—bronchi, larynx, nasal cavity, alveoli, Mechanics of Breathing trachea, pharynx, bronchioles. Breathing, or pulmonary ventilation, is a mechani- 4. Which main bronchus is the most likely site for an inhaled object to become lodged? Why? cal process that depends on volume changes 5. The lungs are mostly passageways and elastic tissue. occurring in the thoracic cavity. Keep this rule in What is the role of the passageways? Of the elastic mind about the mechanics of breathing: Volume tissue? changes lead to pressure changes, which lead to the 6. Name the four structures that make up the respiratory flow of gases to equalize the pressure. zone. A gas, like a liquid, always conforms to the For answers, see Appendix A. shape of its container. However, unlike a liquid, a gas fills its container. Therefore, in a large volume, Respiratory Physiology the gas molecules will be far apart, and the pres- sure (created by the gas molecules hitting each ➔ Learning Objectives other and the walls of the container) will be low. □□ Define cellular respiration, external respiration, Assuming the amount of gas remains constant, if internal respiration, pulmonary ventilation, the volume is reduced, the gas molecules will be expiration, and inspiration. closer together, and the pressure will rise. ➔ □□ Explain how the respiratory muscles cause volume changes that lead to air flow into and out of the ConceptLink lungs (breathing). Recall that pressure changes also drive other processes The major function of the respiratory system is to in the body, such as filtration (passive transport; supply the body with oxygen and to dispose of Chapter 3, pp. 102–103) and blood flow (Chapter 11). carbon dioxide. To do this, at least four distinct In these processes, substances move from high to low events, collectively called respiration, must occur: pressure and achieve a specific function, such as mem- brane transport or circulation. 1. Pulmonary ventilation. Air must move into and out of the lungs so that the gases Let’s see how volume changes relate to the in the alveoli of the lungs are continuously two phases of breathing—inspiration, when air is refreshed. This process of pulmonary ventila- flowing into the lungs, and expiration, when air tion is commonly called breathing. is leaving the lungs. 2. External respiration. Gas exchange (oxy- gen loading and carbon dioxide unloading) Inspiration Copyright © 2017. Pearson Education Limited. All rights reserved. between the pulmonary blood and alveoli When the inspiratory muscles, the diaphragm must take place. Remember that in external and external intercostals, contract, the size of respiration, gas exchanges are being made the thoracic cavity increases. As the dome-shaped between the blood and the body exterior. diaphragm contracts inferiorly, the superior-­ 3. Respiratory gas transport. Oxygen and car- inferior dimension (height) of the thoracic cavity bon dioxide must be transported to and from increases (Figure 13.7a, p. 472). Contraction of the the lungs and tissue cells of the body via the external intercostals lifts the rib cage and thrusts bloodstream. the sternum forward, which increases the antero- posterior and lateral dimensions of the thorax. The 13 4. Internal respiration. At systemic capillaries, lungs adhere tightly to the thorax walls (because of gas exchange occurs between the blood and the surface tension of the fluid between the cells inside the body. pleural membranes), so they are stretched to the Although only the first two processes are the new, larger size of the thorax. As intrapulmonary special responsibility of the respiratory system, all volume (the volume within the lungs) increases, four processes are necessary for gas exchange to the gases within the lungs spread out to fill occur. Note that cellular respiration, the use of the larger space. The resulting decrease in gas Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 472 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. 472 Essentials of Human Anatomy and Physiology Changes in anterior-posterior and Changes in lateral dimensions superior-inferior dimensions Ribs are elevated as external intercostals contract External Full inspiration intercostal (External muscles intercostals contract) Diaphragm moves inferiorly during contraction (a) Inspiration: Air (gases) flows into the lungs Ribs are depressed as external intercostals relax External Expiration intercostal (External muscles intercostals relax) Copyright © 2017. Pearson Education Limited. All rights reserved. Diaphragm moves superiorly as it relaxes (b) Expiration: Air (gases) flows out of the lungs Figure 13.7 Rib cage and elevated, and diaphragm is depressed. dimension is reduced; the rib cage is diaphragm positions during Lungs are stretched to the larger descended; and the diaphragm is breathing. Black arrows represent thoracic volume, causing the elevated and dome-shaped. Lungs the direction of diaphragm intrapulmonary pressure to fall and recoil to a smaller volume, movement. (a) At the end of a air to flow into the lungs. (b) At the intrapulmonary pressure rises, and air normal inspiration: Chest is end of a normal expiration: The chest flows out of the lungs. expanded laterally, rib cage is is depressed, and the lateral Marieb, Elaine N., and Suzanne M. Keller. Essentials of Human Anatomy & Physiology, Global Edition, Pearson Education Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/bangor/detail.action?docID=5186375. Created from bangor on 2020-12-03 02:48:47.  M13_MARI6119_12_GE_C13.indd Page 473 5/2/17 6:37 PM s-w-149 /203/PH03344/9781292216119_MARIEB/MARIEB_ESSENTIALS_OF_HUMAN_ANATOMY_AND_PHYSIOLO. Chapter 13: The Respiratory System 473 Inspiration Expiration than atmospheric pressure (see Figure 13.8a). This to atmospheric pressure +2 causes the gases to passively flow out to equalize Intrapulmonary the pressure with the o