Respiratory System PDF

CHAPTER 23 The Respiratory System The Respiratory System and Homeostasis The respiratory system contributes to homeostasis by providing for the exchange of gases—oxygen and carbon dioxide—between the atmospheric air, blood, and tissue cells. It also helps adjust the pH of body fluids. Your b...

CHAPTER 23 The Respiratory System The Respiratory System and Homeostasis The respiratory system contributes to homeostasis by providing for the exchange of gases—oxygen and carbon dioxide—between the atmospheric air, blood, and tissue cells. It also helps adjust the pH of body fluids. Your body’s cells continually use oxygen (O2) for the metabolic starvation and buildup of waste products. In addition to functioning reactions that generate ATP from the breakdown of nutrient in gas exchange, the respiratory system also participates in regulating molecules. At the same time, these reactions release carbon blood pH, contains receptors for the sense of smell, filters inspired dioxide (CO2) as a waste product. Because an excessive amount of air, produces sounds, and rids the body of some water and heat in CO2 produces acidity that can be toxic to cells, excess CO2 must be exhaled air. As in the digestive and urinary systems, which will be eliminated quickly and efficiently. The cardiovascular and respiratory covered in subsequent chapters, in the respiratory system there is systems cooperate to supply O2 and eliminate CO2. The respiratory an extensive area of contact between the external environment and system provides for gas exchange—intake of O2 and elimination of capillary blood vessels. CO2—and the cardiovascular system transports blood containing the gases between the lungs and body cells. Failure of either system Q Did you ever wonder how smoking affects the respiratory disrupts homeostasis by causing rapid death of cells from oxygen system? 850  23.1 Overview of the Respiratory System 851 FIGURE 23.1 The three basic steps involved in respiration. 23.1 Overview of the Respiratory System During respiration, the body is supplied with O2, and CO2 is removed. CO2 exhaled 1 Pulmonary OBJECTIVES O2 inhaled ventilation (breathing) Discuss the steps that occur during respiration. Define the respiratory system. Explain how the respiratory organs are classified structurally and Alveoli functionally. of lungs CO2 O2 2 External (pulmonary) respiration Pulmonary CO2 capillaries O2 The Steps Involved in Respiration The process of supplying the body with O2 and removing CO2 is known as respiration, which has three basic steps (Figure 23.1): Pulmonary circulation 1 Pulmonary ventilation (pulmon- = lung), or breathing, is the inhalation (inflow) and exhalation (outflow) of air and involves the exchange of air between the atmosphere and the alveoli of the lungs. Inhalation permits O2 to enter the lungs and exhalation permits CO2 to leave the lungs. 2 External (pulmonary) respiration is the exchange of gases Transport of between the alveoli of the lungs and the blood in pulmonary O2 and CO2 by the blood capillaries across the respiratory membrane. In this process, pulmonary capillary blood gains O2 and loses CO2. 3 Internal (tissue) respiration is the exchange of gases between blood in systemic capillaries and tissue cells. In this step the Systemic circulation blood loses O2 and gains CO2. Within cells, the metabolic reactions that consume O2 and give off CO2 during the production of ATP are termed cellular respiration (discussed in Chapter 25). O2 Systemic CO2 capillaries 3 Internal (tissue) respiration Components of the Respiratory System Nutrient + O CO2 + H2O + ATP molecule 2 The respiratory system (RES-pi-ra-tōr-ē) consists of the nose, Cellular respiration pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and Systemic tissue cells lungs (Figure 23.2). Its parts can be classified according to either structure or function. Structurally, the respiratory system consists of Q How does external respiration differ from internal two parts: (1) The upper respiratory system includes the nose, nasal respiration? cavity, pharynx, and associated structures; (2) the lower respiratory system includes the larynx, trachea, bronchi, and lungs. Function- ally, the respiratory system also consists of two parts. (1) The con- ducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, and alveoli and are the main sites of gas exchange between air and nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and ter- blood. minal bronchioles; their function is to filter, warm, and moisten air The branch of medicine that deals with the diagnosis and treat- and conduct it into the lungs. (2) The respiratory zone consists of ment of diseases of the ears, nose, and throat (ENT) is called otorhi- tubes and tissues within the lungs where gas exchange occurs. These nolaryngology (ō′-tō-rī′-nō-lar-in-GOL-o-jē; oto- = ear; -rhino- = include the respiratory bronchioles, alveolar ducts, alveolar sacs, nose; -laryngo- = voice box; -logy = study of). FIGURE 23.2 Structures of the respiratory system. The upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures; the lower respiratory system includes the larynx, trachea, bronchi, and lungs. Functions of the respiratory system 1. Provides for gas exchange: intake 3. Contains receptors for sense of of O2 for delivery to body cells and smell, filters inspired air, produces removal of CO2 produced by body vocal sounds (phonation), and cells. excretes small amounts of water Nose: 2. Helps regulate blood pH. and heat. External Nasal cavity (internal) Pharynx Larynx Trachea Right main bronchus Lungs (a) Anterior view showing organs of respiration Larynx Right common carotid artery Thyroid gland Anterior scalene muscle Trachea Subclavian artery Right subclavian artery Phrenic nerve Brachiocephalic artery Left common carotid artery Superior vena cava Arch of aorta Dissection Shawn Miller, Photograph Mark Nielsen Rib (cut) Right lung Left lung Heart in pericardial sac Liver Diaphragm (b) Anterior view of lungs and heart after removal of the anterolateral thoracic wall and pleura Q Which structures are part of the conducting zone of the respiratory system? 852  23.2 The Upper Respiratory System 853 external nose consists of several pieces of hyaline cartilage connected Checkpoint to each other and certain skull bones by fibrous connective tissue. 1. What are the three basic steps involved in respiration? The components of the cartilaginous framework are the septal nasal 2. What are the components of the respiratory system? cartilage, which forms the anterior portion of the nasal septum; the lateral nasal cartilages inferior to the nasal bones; and the alar car- 3. Why is the respiratory zone important? - tilages (A -lar), which form a portion of the walls of the nostrils. Because it consists of pliable hyaline cartilage, the cartilaginous framework of the external nose is somewhat flexible. On the under- surface of the external nose are two openings called the external 23.2 The Upper Respiratory - nares (NA -rez; singular is naris) or nostrils, which lead into cavities called the nasal vestibules. Figure 23.4 shows the surface anatomy System of the nose. The interior structures of the external nose have three functions: (1) warming, moistening, and filtering incoming air; (2) detecting ol- OBJECTIVES factory stimuli; and (3) modifying speech vibrations as they pass through the large, hollow resonating chambers. Resonance refers to Describe the anatomy and histology of the nose, pharynx and prolonging, amplifying, or modifying a sound by vibration. associated structures. Identify the functions of these respiratory structures. Clinical Connection Rhinoplasty Nose - Rhinoplasty (RI-nō-plas′-tē; thin = nose; -plasty = to mold or to shape), or “nose job,” is a surgical procedure in which the shape of the external The nose is a specialized organ at the entrance of the respiratory sys- nose is altered. Although rhinoplasty is often done for cosmetic reasons, tem that consists of a visible external portion (external nose) and an it is sometimes performed to repair a fractured nose or a deviated nasal internal portion inside the skull called the nasal cavity (internal nose). septum. In the procedure, both local and general anesthetics are given. The external nose is the portion of the nose visible on the face and Instruments are then inserted through the nostrils, the nasal cartilage is consists of a supporting framework of bone and hyaline cartilage cov- reshaped, and the nasal bones are fractured and repositioned to achieve ered with muscle and skin and lined by a mucous membrane. The the desired shape. An internal packing and splint are inserted to keep the frontal bone, nasal bones, and maxillae form the bony framework of nose in the desired position as it heals. the external nose (Figure 23.3a). The cartilaginous framework of the FIGURE 23.3 Respiratory structures in the head and neck. As air passes through the nose, it is warmed, filtered, and moistened; and olfaction occurs. Bony framework: Frontal bone Nasal bones Maxilla Cartilaginous framework: Lateral nasal cartilages Septal nasal cartilage Minor alar cartilages Major alar cartilages Dense fibrous connective and adipose tissue (a) Anterolateral view of nose showing cartilaginous and bony frameworks Figure 23.3 Continues 854 CH APTE R 2 3 The Respiratory System FIGURE 23.3 Continued Parasagittal plane Superior Nasal meatuses Middle Frontal sinus Inferior Frontal bone Olfactory epithelium Sphenoid bone Nasal bone Sphenoidal sinus Superior Internal naris Middle Nasal Pharyngeal tonsil Inferior conchae Nasopharynx Nasal vestibule Opening of auditory External naris tube Maxilla Uvula Palatine tonsil Oral cavity Fauces Tongue Palatine bone Oropharynx Soft palate Lingual tonsil Epiglottis Mandible Hyoid bone Laryngopharynx Vestibular fold (false vocal cord) Vocal fold (true vocal cord) Regions of the pharynx Larynx Esophagus Nasopharynx Thyroid cartilage Oropharynx Trachea Cricoid cartilage Thyroid gland Laryngopharynx (b) Parasagittal section of left side of head and neck showing location of respiratory structures Sagittal plane Frontal sinus View Superior nasal concha Superior nasal meatus Middle nasal concha Sphenoidal sinus Middle nasal meatus Inferior nasal concha Inferior nasal meatus Hard palate (c) Medial view of sagittal section  23.2 The Upper Respiratory System 855 Frontal plane View Brain Optic nerve Ethmoidal cells Periorbital fat Superior nasal concha Superior nasal meatus Nasal septum: Middle nasal concha Perpendicular Middle nasal meatus plate of ethmoid Maxillary sinus Vomer Inferior nasal concha Inferior nasal meatus Hard palate Tongue Dissection Shawn Miller, Photograph Mark Nielsen (d) Frontal section showing conchae Q What is the path taken by air molecules into and through the nose? FIGURE 23.4 Surface anatomy of the nose. The nasal cavity (internal nose) is a large space in the anterior as- pect of the skull that lies inferior to the nasal bone and superior to the The external nose has a cartilaginous framework and a bony framework. oral cavity; it is lined with muscle and mucous membrane. A vertical par- tition, the nasal septum, divides the nasal cavity into right and left sides. The anterior portion of the nasal septum consists primarily of hyaline cartilage; the remainder is formed by the vomer and the perpendicular plate of the ethmoid, maxillae, and palatine bones (see Figure 7.11). Anteriorly, the nasal cavity merges with the external nose, and pos- teriorly it communicates with the pharynx through two openings called - 1 the internal nares or choanae (kō-A -nē) (see Figure 23.3b). Ducts from 3 the paranasal sinuses (which drain mucus) and the nasolacrimal ducts (which drain tears) also open into the nasal cavity. Recall from Chapter 2 4 7 that the paranasal sinuses are cavities in certain cranial and facial bones lined with mucous membrane that are continuous with the lining of the nasal cavity. Skull bone, containing the paranasal sinuses are the frontal, sphenoid, ethmoid, and maxillae. Besides producing mucus, the paranasal sinuses serve as resonating chambers for sound as we speak or sing. The lateral walls of the internal nose are formed by the ethmoid, maxillae, lacrimal, palatine, and inferior nasal conchae bones (see Figure 7.9); the ethmoid bone also forms the roof. The palatine Courtesy Lyne Marie Borghesi bones and palatine processes of the maxillae, which together consti- Anterior view tute the hard palate, form the floor of the internal nose. The bony and cartilaginous framework of the nose help to keep 1. Root: Superior attachment of the nose to the frontal bone 2. Apex: Tip of nose the vestibule and nasal cavity patent, that is, open or unobstructed. 3. Bridge: Bony framework of nose formed by nasal bones The nasal cavity is divided into a larger, inferior respiratory region and 4. External naris: Nostril; external opening into nasal cavity a smaller, superior olfactory region. The respiratory region is lined Q Which part of the nose is attached to the frontal bone? with ciliated pseudostratified columnar epithelium with numerous 856 CH APTE R 2 3 The Respiratory System goblet cells, which is frequently called the respiratory epithelium The superior portion of the pharynx, called the nasopharynx, (see Table 4.1). The anterior portion of the nasal cavity just inside the lies posterior to the nasal cavity and extends to the soft palate. The nostrils, called the nasal vestibule, is surrounded by cartilage; the soft palate, which forms the posterior portion of the roof of the superior part of the nasal cavity is surrounded by bone. mouth, is an arch-shaped muscular partition between the naso- When air enters the nostrils, it passes first through the vestibule, pharynx and oropharynx that is lined by mucous membrane. There which is lined by skin containing coarse hairs that filter out large dust are five openings in its wall: two internal nares, two openings that particles. Three shelves formed by projections of the superior, middle, lead into the auditory (pharyngotympanic) tubes (commonly known and inferior nasal conchae extend out of each lateral wall of the as the eustachian tubes), and the opening into the oropharynx. The nasal cavity. The conchae, almost reaching the nasal septum, subdi- posterior wall also contains the pharyngeal tonsil (fa-RIN-je-al), or vide each side of the nasal cavity into a series of groovelike air pas- adenoid. Through the internal nares, the nasopharynx receives air sageways—the superior, middle, and inferior nasal meatuses (mē- from the nasal cavity along with packages of dust-laden mucus. The - A -tus-ēz = openings or passages; singular is meatus). Mucous nasopharynx is lined with ciliated pseudostratified columnar epithe- membrane lines the nasal cavity and its shelves. The arrangement of lium, and the cilia move the mucus down toward the most inferior conchae and meatuses increases surface area in the internal nose and part of the pharynx. The nasopharynx also exchanges small amounts prevents dehydration by trapping water droplets during exhalation. of air with the auditory tubes to equalize air pressure between the middle ear and the atmosphere. Clinical Connection The intermediate portion of the pharynx, the oropharynx, lies posterior to the oral cavity and extends from the soft palate inferiorly Tonsillectomy to the level of the hyoid bone. It has only one opening into it, the fau- Tonsillectomy (ton-si-LEK-tō-mē-; -ektome = excision or to cut out) is ces (FAW-sēz = throat), the opening from the mouth. This portion of surgical removal of the tonsils. The procedure is usually performed under the pharynx has both respiratory and digestive functions, serving as a general anesthesia on an outpatient basis. Tonsillectomies are performed common passageway for air, food, and drink. Because the oropharynx - in individuals who have frequent tonsillitis (ton′-si-LI-tis), that is, inflam- is subject to abrasion by food particles, it is lined with nonkeratinized mation of the tonsils; tonsils that develop an abscess or tumor; or tonsils stratified squamous epithelium. Two pairs of tonsils, the palatine and that obstruct breathing during sleep. lingual tonsils, are found in the oropharynx. The inferior portion of the pharynx, the laryngopharynx (la- As inhaled air whirls around the conchae and meatuses, it is RING-gō-far-ingks), or hypopharynx, begins at the level of the hyoid warmed by blood in the capillaries. Mucus secreted by the goblet cells bone. At its inferior end it opens into the esophagus (food tube) pos- moistens the air and traps dust particles. Drainage from the nasolacri- teriorly and the larynx (voice box) anteriorly. Like the oropharynx, the mal ducts also helps moisten the air, and is sometimes assisted by secre- laryngopharynx is both a respiratory and a digestive pathway and is tions from the paranasal sinuses. The cilia move the mucus and trapped lined by nonkeratinized stratified squamous epithelium. dust particles toward the pharynx, at which point they can be swallowed or spit out, thus removing the particles from the respiratory tract. Checkpoint The olfactory receptor cells, supporting cells, and basal cells lie in 4. Compare the structure and functions of the external nose and the respiratory region, which is near the superior nasal conchae and the internal nose. adjacent septum. These cells make up the olfactory epithelium. It 5. What are the functions of the three subdivisions of the pharynx. contains cilia but no goblet cells. Pharynx 23.3 The Lower Respiratory The pharynx (FAR-inks), or throat, is a funnel-shaped tube about 13 cm (5 in.) long that starts at the internal nares and extends to the level of System the cricoid cartilage, the most inferior cartilage of the larynx (voice box) (see Figure 23.3b). The pharynx lies just posterior to the nasal OBJECTIVES and oral cavities, superior to the larynx, and just anterior to the cervi- cal vertebrae. Its wall is composed of skeletal muscles and is lined with Identity the features and purpose of the larynx. a mucous membrane. Relaxed skeletal muscles help keep the pharynx List the structures of voice production. patent. Contraction of the skeletal muscles assists in deglutition (swal- lowing). The pharynx functions as a passageway for air and food, pro- Describe the anatomy and histology of the trachea. vides a resonating chamber for speech sounds, and houses the tonsils, Identify the functions of each bronchial structure. which participate in immunological reactions against foreign invaders. The pharynx can be divided into three anatomical regions: (1) na- sopharynx, (2) oropharynx, and (3) laryngopharynx. (See the lower Larynx orientation diagram in Figure 23.3b.) The muscles of the entire pharynx are arranged in two layers, an outer circular layer and an The larynx (LAR-ingks), or voice box, is a short passageway that con- inner longitudinal layer. nects the laryngopharynx with the trachea. It lies in the midline of the  23.3 The Lower Respiratory System 857 neck anterior to the esophagus and the fourth through sixth cervical cartilages are the most important because they influence changes in vertebrae (C4–C6). position and tension of the vocal folds (true vocal cords for speech). The wall of the larynx is composed of nine pieces of cartilage The extrinsic muscles of the larynx connect the cartilages to other (Figure 23.5). Three occur singly (thyroid cartilage, epiglottis, and structures in the throat; the intrinsic muscles connect the cartilages to cricoid cartilage), and three occur in pairs (arytenoid, cuneiform, one another. The cavity of the larynx is the space that extends from and corniculate cartilages). Of the paired cartilages, the arytenoid the entrance into the larynx down to the inferior border of the cricoid FIGURE 23.5 The larynx. The larynx is composed of nine pieces of cartilage. Epiglottis Hyoid bone Thyrohyoid membrane Epiglottis: Leaf Stem Larynx Thyroid Corniculate cartilage gland Thyroid cartilage (Adam’s apple) Arytenoid cartilage Cricothyroid ligament Cricoid cartilage Cricotracheal ligament Thyroid gland Parathyroid glands (4) Tracheal cartilage (a) Anterior view (b) Posterior view Epiglottis Hyoid bone Sagittal Thyrohyoid membrane plane Thyrohyoid membrane Cuneiform cartilage Fat body Corniculate cartilage Vestibular fold Arytenoid cartilage Thyroid cartilage Laryngeal sinus Vocal fold Cricoid cartilage Cricothyroid ligament Cricotracheal ligament Tracheal cartilage ANTERIOR (c) Sagittal section Figure 23.5 Continues 858 CH APTE R 2 3 The Respiratory System FIGURE 23.5 Continued Frontal plane View Epiglottic cartilage Thyrohyoid muscle Hyoid bone Laryngeal vestibule Vestibular fold Thyrohyoid membrane Thyroepiglottic muscle Vocal fold Rima vestibuli Vocalis muscle Laryngeal ventricle Inferior pharyngeal Thyroid cartilage constrictor muscle Sternothyroid muscle Rima glottidis Infraglottic Lateral cricoarytenoid cavity muscle Cricoid cartilage Cricothyroid muscle Cricotracheal ligament First tracheal cartilage Trachea Thyroid gland Parathyroid gland (d) Frontal section Q How does the epiglottis prevent aspiration of foods and liquids? - cartilage (described shortly). The portion of the cavity of the larynx glottidis (RI-ma GLOT-ti-dis). The closing of the larynx in this way dur- above the vestibular folds (false vocal cords) is called the laryngeal ing swallowing routes liquids and foods into the esophagus and keeps vestibule. The portion of the cavity of the larynx below the vocal folds them out of the larynx and airways. When small particles of dust, is called the infraglottic cavity (infra- = below) (Figure 23.5d). smoke, food, or liquids pass into the larynx, a cough reflex occurs, The thyroid cartilage (Adam’s apple) consists of two fused usually expelling the material. - plates of hyaline cartilage that form the anterior wall of the larynx The cricoid cartilage (KRI-koyd = ringlike) is a ring of hyaline and give it a triangular shape. It is present in both males and fe- cartilage that forms the inferior wall of the larynx. It is attached to the males but is usually larger in males due to the influence of male sex first ring of cartilage of the trachea by the cricotracheal ligament - hormones on its growth during puberty. The ligament that connects (krī′-kō-TRA -kē-al). The thyroid cartilage is connected to the cricoid the thyroid cartilage to the hyoid bone is called the thyrohyoid cartilage by the cricothyroid ligament. The cricoid cartilage is the membrane. landmark for making an emergency airway called a tracheotomy (see The epiglottis (epi- = over; -glottis = tongue) is a large, leaf- Clinical Connection: Tracheotomy and Intubation). - shaped piece of elastic cartilage that is covered with epithelium (see The paired arytenoid cartilages (ar′-i-TE-noyd = ladlelike) are also Figure 23.3b). The “stem” of the epiglottis is the tapered inferior triangular pieces of mostly hyaline cartilage located at the posterior, portion that is attached to the anterior rim of the thyroid cartilage. superior border of the cricoid cartilage. They form synovial joints with The broad superior “leaf” portion of the epiglottis is unattached and the cricoid cartilage and have a wide range of mobility. is free to move up and down like a trap door. During swallowing, the The paired corniculate cartilages (kor-NIK-ū-lāt = shaped like a pharynx and larynx rise. Elevation of the pharynx widens it to receive small horn), horn-shaped pieces of elastic cartilage, are located at the food or drink; elevation of the larynx causes the epiglottis to move apex of each arytenoid cartilage. The paired cuneiform cartilages down and form a lid over the glottis, closing it off. The glottis consists (KŪ-nē-i-form = wedge-shaped), club-shaped elastic cartilages ante- of a pair of folds of mucous membrane, the vocal folds (true vocal rior to the corniculate cartilages, support the vocal folds and lateral cords) in the larynx, and the space between them called the rima aspects of the epiglottis.  23.3 The Lower Respiratory System 859 The lining of the larynx superior to the vocal folds is nonkerati- The vocal folds are the principal structures of voice production. nized stratified squamous epithelium. The lining of the larynx inferior Deep to the mucous membrane of the vocal folds, which is non- to the vocal folds is ciliated pseudostratified columnar epithelium keratinized stratified squamous epithelium, are bands of elastic lig- consisting of ciliated columnar cells, goblet cells, and basal cells. The aments stretched between the rigid cartilages of the larynx like the mucus produced by the goblet cells helps trap dust not removed in strings on a guitar. Intrinsic laryngeal muscles attach to both the the upper passages. The cilia in the upper respiratory tract move mu- rigid cartilages and the vocal folds. When the muscles contract they cus and trapped particles down toward the pharynx; the cilia in the move the cartilages, which pulls the elastic ligaments tight, and this lower respiratory tract move them up toward the pharynx. stretches the vocal folds out into the airways so that the rima glot- tidis is narrowed. Contracting and relaxing the muscles varies the The Structures of Voice Production tension in the vocal folds, much like loosening or tightening a guitar string. Air passing through the larynx vibrates the folds and produces The mucous membrane of the larynx forms two pairs of folds (Figure sound (phonation) by setting up sound waves in the column of air in 23.5c): a superior pair called the vestibular folds (false vocal cords) the pharynx, nose, and mouth. The variation in the pitch of the and an inferior pair called the vocal folds (true vocal cords). The space sound is related to the tension in the vocal folds. The greater the between the vestibular folds is known as the rima vestibuli. The pressure of air, the louder the sound produced by the vibrating vocal laryngeal ventricle is a lateral expansion of the middle portion of the folds. laryngeal cavity inferior to the vestibular folds and superior to the When the intrinsic muscles of the larynx contract, they pull on vocal folds (see Figure 23.3b). While the vestibular folds do not func- the arytenoid cartilages, which causes the cartilages to pivot and tion in voice production, they do have other important functional slide. Contraction of the posterior cricoarytenoid muscles, for exam- roles. When the vestibular folds are brought together, they function in ple, moves the vocal folds apart (abduction), thereby opening the holding the breath against pressure in the thoracic cavity, such as rima glottidis (Figure 23.6a). By contrast, contraction of the lateral might occur when a person strains to lift a heavy object. cricoarytenoid muscles moves the vocal folds together (adduction), FIGURE 23.6 Movement of the vocal folds. The glottis consists of a pair of folds of mucous membrane in the larynx (the vocal folds) and the space between them (the rima glottidis). Tongue Thyroid cartilage Epiglottis Glottis: Cricoid cartilage Vocal folds Vocal ligament Rima glottidis Vestibular folds Arytenoid cartilage Cuneiform cartilage Corniculate cartilage Posterior cricoarytenoid Superior view of cartilages muscle View through a laryngoscope and muscles (a) Movement of vocal folds apart (abduction) View Larynx Lateral cricoarytenoid muscle (b) Movement of vocal folds together (adduction) Q What is the main function of the vocal folds? 860 CH APTE R 2 3 The Respiratory System thereby closing the rima glottidis (Figure 23.6b). Other intrinsic Clinical Connection muscles can elongate (and place tension on) or shorten (and relax) the vocal folds. Pitch is controlled by the tension on the vocal folds. If they are Laryngitis and Cancer of the Larynx pulled taut by the muscles, they vibrate more rapidly, and a higher Laryngitis is an inflammation of the larynx that is most often caused by pitch results. Decreasing the muscular tension on the vocal folds a respiratory infection or irritants such as cigarette smoke. Inflammation causes them to vibrate more slowly and produce lower-pitched of the vocal folds causes hoarseness or loss of voice by interfering with sounds. Due to the influence of androgens (male sex hormones), vocal the contraction of the folds or by causing them to swell to the point where they cannot vibrate freely. Many long-term smokers acquire a permanent folds are usually thicker and longer in males than in females, and hoarseness from the damage done by chronic inflammation. Cancer of the therefore they vibrate more slowly. This is why a man’s voice generally larynx is found almost exclusively in individuals who smoke. The condition has a lower range of pitch than that of a woman. is characterized by hoarseness, pain on swallowing, or pain radiating to an Sound originates from the vibration of the vocal folds, but other ear. Treatment consists of radiation therapy and/or surgery. structures are necessary for converting the sound into recognizable speech. The pharynx, mouth, nasal cavity, and paranasal sinuses all act as resonating chambers that give the voice its human and indi- vidual quality. We produce the vowel sounds by constricting and Trachea relaxing the muscles in the wall of the pharynx. Muscles of the face, - tongue, and lips help us enunciate words. The trachea (TRA -kē-a = sturdy), or windpipe, is a tubular passageway Whispering is accomplished by closing all but the posterior por- for air that is about 12 cm (5 in.) long and 2.5 cm (1 in.) in diameter. It is tion of the rima glottidis. Because the vocal folds do not vibrate during located anterior to the esophagus (Figure 23.7) and extends from the whispering, there is no pitch to this form of speech. However, we can larynx to the superior border of the fifth thoracic vertebra (T5), where it still produce intelligible speech while whispering by changing the divides into right and left primary bronchi (see Figure 23.8). shape of the oral cavity as we enunciate. As the size of the oral cavity The layers of the tracheal wall, from deep to superficial, are the changes, its resonance qualities change, which imparts a vowel-like (1) mucosa, (2) submucosa, (3) hyaline cartilage, and (4) adventitia pitch to the air as it rushes toward the lips. (composed of areolar connective tissue). The mucosa of the trachea FIGURE 23.7 Location of the trachea in relation to the esophagus. The trachea is anterior to the esophagus and extends from the larynx to the superior border of the fifth thoracic vertebra. Esophagus Trachea ANTERIOR Transverse plane Tracheal cartilage Right lateral lobe of thyroid gland Left lateral lobe Trachealis muscle of thyroid gland in fibromuscular membrane Esophagus Dissection Shawn Miller, Photograph Mark Nielsen (a) Superior view of transverse section of thyroid gland, trachea, and esophagus Ciliated epithelial cell Goblet cell NIBSC/Science Source Images SEM about 1100x Q What is the benefit of not having complete rings of tracheal cartilage (b) Epithelial surface of trachea between the trachea and the esophagus?  23.3 The Lower Respiratory System 861 FIGURE 23.8 Branching of airways from the trachea. The bronchial tree consists of macroscopic airways that begin at the trachea and continue through the terminal bronchioles. BRANCHING OF BRONCHIAL TREE Larynx Trachea Trachea Main bronchi Lobar bronchi Right lung Left lung Segmental bronchi Visceral pleura Bronchioles Parietal pleura Terminal bronchioles Pleural cavity Location of carina Right main bronchus Left main bronchus Right lobar Left lobar bronchus bronchus Left segmental bronchus Right segmental Left bronchiole bronchus Right bronchiole Left terminal bronchiole Right terminal bronchiole Cardiac notch Diaphragm (a) Anterior view of bronchial tree Airway branching Names of branches Generation # Trachea 0 Main bronchi 1 Lobar and segmental bronchi Conducting zone 2–10 Bronchioles and terminal 11–16 bronchioles Respiratory 17–19 bronchioles Respiratory zone Alveolar ducts 20–22 Alveolar sacs 23 Q How many lobes and secondary bronchi are (b) Airway branching present in each lung? 862 CH APTE R 2 3 The Respiratory System consists of an epithelial layer of ciliated pseudostratified columnar epi- is formed by a posterior and somewhat inferior projection of the last thelium and an underlying layer of lamina propria that contains elastic tracheal cartilage. The mucous membrane of the carina is one of the and reticular fibers. It provides the same protection against dust as the most sensitive areas of the entire larynx and trachea for triggering a membrane lining the nasal cavity and larynx. The submucosa consists of cough reflex. Widening and distortion of the carina is a serious sign areolar connective tissue that contains seromucous glands and their because it usually indicates a carcinoma of the lymph nodes around ducts. the region where the trachea divides. The 16–20 incomplete, horizontal rings of hyaline cartilage On entering the lungs, the main bronchi divide to form smaller resemble the letter C, are stacked one above another, and are con- bronchi—the lobar (secondary) bronchi, one for each lobe of the nected by dense connective tissue. They may be felt through the skin lung. (The right lung has three lobes; the left lung has two.) The lobar inferior to the larynx. The open part of each C-shaped cartilage ring bronchi continue to branch, forming still smaller bronchi, called seg- faces posteriorly toward the esophagus (Figure 23.7) and is spanned mental (tertiary) bronchi (TER-shē-e-rē), that supply the specific by a fibromuscular membrane. Within this membrane are transverse bronchopulmonary segments within the lobes. The segmental bron- - smooth muscle fibers, called the trachealis muscle (trā-kē-A -lis), and chi then divide into bronchioles. Bronchioles in turn branch repeat- elastic connective tissue that allow the diameter of the trachea to edly, and the smallest ones branch into even smaller tubes called ter- change subtly during inhalation and exhalation, which is important in minal bronchioles. These bronchioles contain club (Clara) cells, maintaining efficient airflow. The solid C-shaped cartilage rings provide columnar, nonciliated cells interspersed among the epithelial cells. a semirigid support to maintain patency so that the tracheal wall does Club cells may protect against harmful effects of inhaled toxins and not collapse inward (especially during inhalation) and obstruct the air carcinogens, produce surfactant (discussed shortly), and function as passageway. The adventitia of the trachea consists of areolar connec- stem cells (reserve cells), which give rise to various cells of the epithe- tive tissue that joins the trachea to surrounding tissues. lium. The terminal bronchioles represent the end of the conducting zone of the respiratory system. This extensive branching from the tra- chea through the terminal bronchioles resembles an inverted tree Clinical Connection and is commonly referred to as the bronchial tree. Beyond the termi- nal bronchioles of the bronchial tree, the branches become micro- Tracheotomy and Intubation scopic. These branches are called the respiratory bronchioles and Several conditions may block airflow by obstructing the trachea. The rings alveolar ducts, which will be described shortly (see Figure 23.11). of cartilage that support the trachea may be accidentally crushed, the mu- The respiratory passages from the trachea to the alveolar ducts cous membrane may become inflamed and swell so much that it closes off contain about 23 generations of branching; branching from the tra- the passageway, excess mucus secreted by inflamed membranes may clog chea into main bronchi is called first-generation branching, that from the lower respiratory passages, a large object may be aspirated (breathed main bronchi into lobar bronchi is called second-generation branch- in), or a cancerous tumor may protrude into the airway. Two methods are ing, and so on down to the alveolar ducts (Figure 23.8b). used to reestablish airflow past a tracheal obstruction. If the obstruction As the branching becomes more extensive in the bronchial tree, is above the level of the larynx, a tracheotomy (trā-kē-O-tō-mē) may be several structural changes may be noted. performed. In this procedure, also called a tracheostomy, a skin incision is followed by a short longitudinal incision into the trachea below the cricoid 1. The mucous membrane in the bronchial tree changes from ciliated cartilage. A tracheal tube is then inserted to create an emergency air pas- pseudostratified columnar epithelium in the main bronchi, lobar - sageway. The second method is intubation (in′-too-BA -shun), in which a bronchi, and segmental bronchi to ciliated simple columnar epi- tube is inserted into the mouth or nose and passed inferiorly through the thelium with some goblet cells in larger bronchioles, to mostly cili- larynx and trachea. The firm wall of the tube pushes aside any flexible ob- ated simple cuboidal epithelium with no goblet cells in smaller struction, and the lumen of the tube provides a passageway for air; any bronchioles, to mostly nonciliated simple cuboidal epithelium in mucus clogging the trachea can be suctioned out through the tube. terminal bronchioles. Recall that ciliated epithelium of the respira- tory membrane removes inhaled particles in two ways; mucus pro- duced by goblet cells traps the particles, and the cilia move the Bronchi mucus and trapped particles toward the pharynx for removal. In regions where nonciliated simple cuboidal epithelium is present, At the superior border of the fifth thoracic vertebra, the trachea inhaled particles are removed by macrophages. divides into a right main (primary) bronchus (BRONG-kus = wind- 2. Plates of cartilage gradually replace the incomplete rings of carti- pipe), which goes into the right lung, and a left main (primary) bron- lage in main bronchi and finally disappear in the distal bronchioles. chus, which goes into the left lung (Figure 23.8). The right main 3. As the amount of cartilage decreases, the amount of smooth muscle bronchus is more vertical, shorter, and wider than the left. As a result, increases. Smooth muscle encircles the lumen in spiral bands and an aspirated object is more likely to enter and lodge in the right main helps maintain patency. However, because there is no supporting car- bronchus than the left. Like the trachea, the main bronchi (BRONG-kī) tilage, muscle spasms can close off the airways. This is what happens contain incomplete rings of cartilage and are lined by ciliated pseu- during an asthma attack, which can be a life-threatening situation. dostratified columnar epithelium. At the point where the trachea divides into right and left main During exercise, activity in the sympathetic division of the auto- - bronchi an internal ridge called the carina (ka-RI -na = keel of a boat) nomic nervous system (ANS) increases and the adrenal medulla  23.3 The Lower Respiratory System 863 releases the hormones epinephrine and norepinephrine; both of thoracic cavity; the deep layer, the visceral pleura, covers the lungs these events cause relaxation of smooth muscle in the bronchioles, themselves (Figure 23.9). Between the visceral and parietal pleurae is a which dilates the airways. Because air reaches the alveoli more small space, the pleural cavity, which contains a small amount of quickly, lung ventilation improves. The parasympathetic division of lubricating fluid secreted by the membranes. This pleural fluid reduces the ANS and mediators of allergic reactions such as histamine have friction between the membranes, allowing them to slide easily over one the opposite effect, causing contraction of bronchiolar smooth mus- another during breathing. Pleural fluid also causes the two membranes cle, which results in constriction of distal bronchioles. to adhere to one another just as a film of water causes two glass micro- scope slides to stick together, a phenomenon called surface tension. Separate pleural cavities surround the left and right lungs. Inflamma- Checkpoint tion of the pleural membrane, called pleurisy or pleuritis, may in its 6. How does the larynx function in respiration and voice production? early stages cause pain due to friction between the parietal and visceral 7. Describe the location, structure, and function of the trachea. layers of the pleura. If the inflammation persists, excess fluid accumu- lates in the pleural space, a condition known as pleural effusion. 8. Describe the structure of the bronchial tree. Clinical Connection Lungs Pneumothorax and Hemothorax A pulmonologist (pul-mō-NOL-ō-gist; pulmo- = lung) is a specialist in In certain conditions, the pleural cavities may fill with air (pneumothorax; the diagnosis and treatment of lung diseases. The lungs (= light- noo′-mō-THOR-aks; pneumo- = air or breath), blood (hemothorax), or pus. weights, because they float) are paired cone-shaped organs in the tho- Air in the pleural cavities, most commonly introduced in a surgical opening racic cavity (Figure 23.9). They are separated from each other by the of the chest or as a result of a stab or gunshot wound, may cause the lungs heart and other structures of the mediastinum, which divides the tho- to collapse. This collapse of a part of a lung, or rarely an entire lung, is called racic cavity into two anatomically distinct chambers. As a result, if atelectasis (at′-e-LEK-ta-sis; ateles- = incomplete; -ectasis = expansion). The trauma causes one lung to collapse, the other may remain expanded. goal of treatment is the evacuation of air (or blood) from the pleural space, Each lung is enclosed and protected by a double-layered serous mem- which allows the lung to reinflate. A small pneumothorax may resolve on its brane called the pleural membrane (PLOOR-al; pleur- = side) or pleura. own, but it is often necessary to insert a chest tube to assist in evacuation. The superficial layer, called the parietal pleura, lines the wall of the FIGURE 23.9 Relationship of the pleural membranes to the lungs. The parietal pleura lines the thoracic cavity, and the visceral pleura covers the lungs. ANTERIOR Transverse plane Sternum Left lung Visceral pleura Ascending aorta Superior vena cava Pulmonary arteries Parietal Pulmonary vein View pleura Right lung Esophagus Pleural Thoracic aorta cavity Body of T4 Spinal cord MEDIAL Dissection Shawn Miller, Photograph Mark Nielsen Inferior view of a transverse section through the thoracic cavity showing the pleural cavity and pleural membranes Q What type of membrane is the pleural membrane? 864 CH APTE R 2 3 The Respiratory System The lungs extend from the diaphragm to just slightly superior to ribs, the costal surface, matches the rounded curvature of the ribs. the clavicles and lie against the ribs anteriorly and posteriorly (Figure The mediastinal (medial) surface of each lung contains a region, the 23.10a). The broad inferior portion of the lung, the base, is concave hilum, through which bronchi, pulmonary blood vessels, lymphatic and fits over the convex area of the diaphragm. The narrow superior vessels, and nerves enter and exit (Figure 23.10e). These structures portion of the lung is the apex. The surface of the lung lying against the are held together by the pleura and connective tissue and constitute FIGURE 23.10 Surface anatomy of the lungs. The oblique fissure divides the left lung into two lobes. The oblique and horizontal fissures divide the right lung into three lobes. First rib Apex of lung Left lung Base of lung Pleural cavity Pleura (a) Anterior view of lungs and pleurae in thorax Apex Superior lobe View (b) View (c) ANTERIOR Horizontal Oblique fissure fissure Oblique fissure Cardiac notch Inferior lobe Middle lobe Inferior lobe POSTERIOR POSTERIOR Base (b) Lateral view of right lung (c) Lateral view of left lung Apex Superior lobe View (d) Oblique fissure View (e) POSTERIOR Hilum and its contents (root) Horizontal fissure Inferior lobe Middle lobe Oblique fissure Cardiac notch ANTERIOR Base ANTERIOR (d) Medial view of right lung (e) Medial view of left lung Q Why are the right and left lungs slightly different in size and shape?  23.3 The Lower Respiratory System 865 the root of the lung. Medially, the left lung also contains a concavity, have an oblique fissure, which extends inferiorly and anteriorly; the the cardiac notch, in which the apex of the heart lies. Due to the space right lung also has a horizontal fissure. The oblique fissure in the left occupied by the heart, the left lung is about 10% smaller than the right lung separates the superior lobe from the inferior lobe. In the right lung. Although the right lung is thicker and broader, it is also some- lung, the superior part of the oblique fissure separates the superior what shorter than the left lung because the diaphragm is higher on the lobe from the inferior lobe; the inferior part of the oblique fissure right side, accommodating the liver that lies inferior to it. separates the inferior lobe from the middle lobe, which is bordered The lungs almost fill the thorax (Figure 23.10a). The apex of the superiorly by the horizontal fissure. lungs lies superior to the medial third of the clavicles, and this is the Each lobe receives its own lobar bronchus. Thus, the right main only area that can be palpated. The anterior, lateral, and posterior sur- bronchus gives rise to three lobar bronchi called the superior, middle, faces of the lungs lie against the ribs. The base of the lungs extends and inferior lobar bronchi, and the left main bronchus gives rise to from the sixth costal cartilage anteriorly to the spinous process of the superior and inferior lobar bronchi. Within the lung, the lobar bronchi tenth thoracic vertebra posteriorly. The pleura extends about 5 cm give rise to the segmental bronchi, which are constant in both origin (2 in.) below the base from the sixth costal cartilage anteriorly to the and distribution—there are 10 segmental bronchi in each lung. The twelfth rib posteriorly. Thus, the lungs do not completely fill the pleural portion of lung tissue that each segmental bronchus supplies is called cavity in this area. Removal of excessive fluid in the pleural cavity can a bronchopulmonary segment (brong-kō-PUL-mō-nār-ē). Bronchial be accomplished without injuring lung tissue by inserting a needle an- and pulmonary disorders (such as tumors or abscesses) that are local- teriorly through the seventh intercostal space, a procedure called ized in a bronchopulmonary segment may be surgically removed - thoracentesis (thor′-a-sen-TE-sis; -centesis = puncture). The needle is without seriously disrupting the surrounding lung tissue. passed along the superior border of the lower rib to avoid damage to Each bronchopulmonary segment of the lungs has many small com- the intercostal nerves and blood vessels. Inferior to the seventh inter- partments called lobules; each lobule is wrapped in elastic connective costal space there is danger of penetrating the diaphragm. tissue and contains a lymphatic vessel, an arteriole, a venule, and a branch from a terminal bronchiole (Figure 23.11a). Terminal bronchioles Lobes, Fissures, and Lobules One or two fissures divide and lobule subdivide into microscopic branches called respiratory each lung into sections called lobes (Figure 23.10b–e). Both lungs bronchioles (Figure 23.11b). They also have alveoli (described shortly) FIGURE 23.11 Microscopic anatomy of a lobule of the lungs. An alveolar sac is the terminal dilation of an alveolar duct and is com- MICROSCOPIC posed of alveoli. AIRWAYS Respiratory bronchioles Alveolar ducts Alveolar sacs Alveoli Terminal bronchiole Pulmonary Pulmonary Terminal arteriole venule bronchiole Lymphatic vessel Respiratory Blood Elastic bronchiole vessel connective tissue Alveoli Respiratory Alveolar bronchiole Biophoto Associates/Science Source Images ducts Alveolar ducts Pulmonary Alveoli capillary Visceral pleura Alveolar Alveolar sac sacs Alveoli Visceral pleura LM about 30x (a) Diagram of a portion of a lobule of the lung (b) Lung lobule Figure 23.11 Continues 866 CH APTE R 2 3 The Respiratory System FIGURE 23.11 Continued Alveolus Pulmonary venule Pulmonary arteriole Bronchiole Dr. Kessel & Dr. Kardon/ tissues & Organs/ SEM 300x Getty Images Q What types of cells make up the wall (c) Section of lung lobule of an alveolus? budding from their walls. Alveoli participate in gas exchange, and thus 2. An epithelial basement membrane underlying the alveolar wall respiratory bronchioles begin the respiratory zone of the respiratory 3. A capillary basement membrane that is often fused to the epithe- system. As the respiratory bronchioles penetrate more deeply into the lial basement membrane lungs, the epithelial lining changes from simple cuboidal to simple squa- 4. The capillary endothelium mous. Respiratory bronchioles in turn subdivide into several (2–11) alveo- - lar ducts (al-VE-ō-lar), which consist of simple squamous epithelium. Alveolar Sacs and Alveoli The terminal dilation of an Clinical Connection - alveolar duct is called an alveolar sac (al-vē-O-lar) and is analogous to a cluster of grapes. Each alveolar sac is composed of outpouchings Coryza, Seasonal Influenza, and H1N1 Influenza - called alveoli (al-vē-O-Iī), analogous to individual grapes (Figure - Hundreds of viruses can cause coryza (ko-RI -za), or the common cold, 23.11). The wall of each alveolus (singular) consists of two types of - but a group of viruses called rhinoviruses (RI-nō-vī-rus-es) is responsible alveolar epithelial cells (Figure 23.12). The more numerous type I for about 40% of all colds in adults. Typical symptoms include sneezing, alveolar (squamous pulmonary epithelial) cells are simple squamous excessive nasal secretion, dry cough, and congestion. The uncomplicated epithelial cells that form a nearly continuous lining of the alveolar wall. common cold is not usually accompanied by a fever. Complications include Type II alveolar cells, also called septal cells, are fewer in number and sinusitis, asthma, bronchitis, ear infections, and laryngitis. Recent investi- are found between type I alveolar cells. The thin type I alveolar cells gations suggest an association between emotional stress and the common are the main sites of gas exchange. Type II alveolar cells, rounded or cold. The higher the stress level, the greater the frequency and duration cuboidal epithelial cells with free surfaces containing microvilli, secrete of colds. Seasonal influenza (flu) is also caused by a virus. Its symptoms alveolar fluid, which keeps the surface between the cells and the air include chills, fever (usually higher than 101°F = 39°C), headache, and muscular aches. Seasonal influenza can become life-threatening and may moist. Included in the alveolar fluid is surfactant (sur-FAK-tant), a develop into pneumonia. It is important to recognize that influenza is a complex mixture of phospholipids and lipoproteins. Surfactant lowers