Upper Respiratory Tract, PDF

23.2 Upper Respiratory Tract The upper respiratory tract, as described previously, includes the nose, nasal cavity, pharynx, and larynx ( figure 23.3a). 23.2a Nose and Nasal Cavity LEARNING OBJECTIVE 5. Describe the structure and function of the nose and nasal cavity. The nose is the first structure...

23.2 Upper Respiratory Tract The upper respiratory tract, as described previously, includes the nose, nasal cavity, pharynx, and larynx ( figure 23.3a). 23.2a Nose and Nasal Cavity LEARNING OBJECTIVE 5. Describe the structure and function of the nose and nasal cavity. The nose is the first structure of the conducting passageway for inhaled air ( figure 23.3b); it is formed by bone, hyaline cartilage, and dense irregular connective tissue covered with skin externally. Paired nasal bones form the bridge of the nose and support it superiorly. Anteroinferiorly from the bridge, there is one pair of lateral cartilages and there are two pairs of alar cartilages. The flared components of the nose are composed of dense irregular connective tissue. The paired nostrils, or nares (nā′res; sing., naris) are the anterior openings that lead into the nasal cavity. The nasal cavity is oblong-shaped, and it extends from the nostrils to paired openings called choanae (kō′an-ē; sing., choana; choane = a funnel) or posterior nasal apertures ( figure 23.3c, d). The choanae are the “doorways” that lead from the nasal cavity into the pharynx. A single choana is labeled in figure 23.3c. The floor of the nasal cavity is formed by the hard and soft palates, and the roof is composed of the nasal, frontal, ethmoid, and sphenoid bones, and some cartilage of the nose (see section 8.2d). The nasal septum divides the nasal cavity into left and right portions ( figure 23.3d). The septum is formed anteriorly by the septal nasal cartilage ( figure 23.3b) and posteriorly by a thin, bony sheet composed of the perpendicular plate of the ethmoid superiorly and the vomer bone inferiorly (see section 8.2d). Note that all of the cartilage in the nose and nasal cavity is hyaline cartilage, which provides a flexible supporting framework for the nose (see section 5.2d). WHAT DO YOU THINK? 1 What is a deviated nasal septum, and how would it affect breathing? Three paired, bony projections are located along the lateral walls of the nasal cavity: the superior, middle, and inferior nasal conchae (kon′kē; sing., concha; a shell) ( figure 23.3c, d). Because the conchae help produce turbulence in the inhaled air, they are sometimes called the turbinate bones. The conchae partition the nasal cavity into separate air passages (or “valleys”), each called a nasal meatus (mē-ā′tŭs). A meatus is located immediately inferior to its corresponding nasal concha. Be careful to distinguish the terms choanae and conchae. Choanae are the openings between the nasal cavity and pharynx; conchae are described here. Figure 23.3 Upper Respiratory Tract. (a) Anatomic regions that compose the upper respiratory tract, (b) supporting structures of the nose, (c) midsagittal section of the nasal cavity, and (d) coronal view of the nasal cavity in a cadaver. (d) ©McGraw-Hill Education/Photo and Dissection by Christine Eckel APR Module 11: Respiratory: Dissection: Nasal Cavity: Coronal: Nasal Septum The nasal cavity is divided into three parts ( figure 23.3c): the nasal vestibule, olfactory region, and respiratory region. The nasal vestibule is immediately internal to the nostrils and is lined by skin and coarse hairs called vibrissae (vi-bris′ē; sing., vibrissa; vibro = to quiver) to trap large particulates. This is the only normally visible portion of the nasal cavity. The olfactory region is the superior portion of the nasal cavity. It contains the olfactory epithelium (which houses the olfactory receptors). Airborne molecules that dissolve in the mucus covering the olfactory epithelium stimulate olfactory receptors to detect different odors (see section 16.3a). The respiratory region of the nasal cavity is lined by a mucosa composed of pseudostratified ciliated columnar epithelium. The lamina propria of this mucosal lining has an extensive vascular network. Nosebleeds (epistaxis) are especially common because of both the vast distribution of blood vessels and their superficial location (just deep to the epithelium), and they are more likely to occur during cold weather because the mucous membranes become dry and crack. Additionally, paired nasolacrimal ducts drain lacrimal secretions from the surface of each eye into the respiratory region of the nasal cavity (see figure 16.9 in section 16.4a). A primary function of the nasal cavity is to condition the air (which means to warm, cleanse, and humidify the air) as it enters the respiratory tract. The air is warmed to body temperature by the extensive array of blood vessels within the nasal cavity lining. These vessels dilate in response to cold air, resulting in increased blood flow that helps to more effectively warm the inhaled air. The air is cleansed as inhaled microbes, dust, and other foreign material become trapped in the mucus covering the inner lining of the respiratory tract. Cilia then “sweep” the mucus and its trapped contents toward the pharynx to be swallowed (see section 22.3a). The air is also humidified as it passes through the moist environment of the nasal passageway. Conditioning of air is enhanced by conchae, which cause air turbulence that increases the amount of contact between the inhaled air and the mucosa ( figure 23.3c, d). Page 896 WHAT DID YOU LEARN? 4 What changes occur to inhaled air as it passes through the nasal cavity? What is the function of the nasal conchae in this process? 23.2b Paranasal Sinuses LEARNING OBJECTIVE 6. Identify the four paired paranasal sinuses and describe their functions. The paranasal (par-ă-nā′săl; para = alongside) sinuses, first described in section 8.2d, are associated with the nasal cavity ( figure 23.4). These sinuses, which are spaces within the skull bones, are named for the specific skull bones in which they are located. Thus, from a superior to inferior direction, they are the paired frontal, ethmoidal, and maxillary sinuses; the sphenoidal sinuses are located posterior to the ethmoidal sinuses. Ducts connect all paranasal sinuses to the nasal cavity. Both the paranasal sinuses and their ducts are lined by a pseudostratified ciliated columnar epithelium that is continuous with the epithelium of the nasal cavity. The mucus, with its trapped particulate matter, is swept by cilia from each paranasal sinus through their ducts into the nasal cavity and then into the pharynx, where it is swallowed. Figure 23.4 Paranasal Sinuses. The paranasal sinuses are air-filled cavities named for the bones in which they occur: frontal, ethmoidal, sphenoidal, and maxillary. APR Module 11: Respiratory: Dissection: Nasal Cavity: Coronal: Maxillary Sinus Like the nasal cavity, the paranasal sinuses also serve to warm and humidify inhaled air, and they also provide a resonance (deep, tonal quality) to the voice. WHAT DID YOU LEARN? 5 How are the paranasal sinuses connected to the nasal cavity? Page 897 INTEGRATE CLINICAL VIEW 23.2 Runny Nose A runny nose, or rhinorrhea (rī΄nō-rē-ă; rhin = nose, rhoia = flow), can occur as a result of (a) an increased production of mucus, such as occurs in response to a cold virus or allergy; (b) crying, due to increased secretions from the lacrimal glands that drain into the nasal cavity; or (c) exposure to cold air. When cold air enters the nasal cavity and is exposed to the warm temperatures, water condensation occurs and the water mixes with mucus. In addition, the watery mucus is more likely to remain within the nasal cavity because the “chilled” cilia on epithelial cells are less able to sweep the mucus into the nasopharynx. INTEGRATE CLINICAL VIEW 23.3 Sinus Infections and Sinus Headaches The mucosa of the ducts that drain from the paranasal sinuses into the nasal cavity can become inflamed in response to a respiratory infection or an allergy; this inflammation of the sinuses is called sinusitis. Drainage of mucus is decreased and mucus accumulates in the paranasal sinuses as a result. A sinus infection can occur due to the lack of proper drainage of mucus. Sinus headaches result from increased pressure within the paranasal sinuses, due to the swelling of the mucosa. They can also result from pressure changes associated with swimming or high altitudes. 23.2c Pharynx LEARNING OBJECTIVE 7. Compare the three regions of the pharynx, and identify and describe their associated structures. The pharynx (far′ingks), commonly called the throat, is a funnel-shaped passageway that averages 13 centimeters (5.1 inches) in length ( figure 23.5). It is located posterior to the nasal cavity, oral cavity, and larynx. Air is conducted along its entire length and food along its inferior portions. The lateral walls of the pharynx are composed of skeletal muscles that both contribute to distensibility (ability to stretch) needed to accommodate swallowed food and help force these materials into the esophagus. The pharynx is partitioned into three regions—from superior to inferior, they are the nasopharynx, oropharynx, and laryngopharynx. Figure 23.5 Pharynx. (a) The three specific regions of the pharynx (nasopharynx, oropharynx, and laryngopharynx) are highlighted in a sagittal section. (b) The pharynx is shown in relationship to the larynx, trachea, and esophagus in an anterolateral view. APR Module 11: Respiratory: Imaging: Upper Respiratory: MRI Sagittal: Nasopharynx Nasopharynx The nasopharynx (nā′zō-far′inks) is the superiormost region of the pharynx. Located directly posterior to the nasal cavity and superior to the soft palate, the nasopharynx, like the nasal cavity, is lined by a pseudostratified ciliated columnar epithelium. Normally, only air passes through the nasopharynx. Material from both the oral cavity and the oropharynx typically is blocked from entering the nasopharynx by the soft palate, which elevates when we swallow (see section 26.2c). However, sometimes food or drink enters the nasopharynx and the nasal cavity, as when a person tries to swallow and then laughs at the same time. The soft palate cannot form a good seal for the nasopharynx, and the force from the laugh may propel some of the material into the nasal cavity. If the laugh is forceful enough, the material may come out the nostrils. The nasopharynx lateral walls have paired openings into auditory tubes (eustachian tubes, or pharyngotympanic tubes) that connect the nasopharynx to the middle ear (see section 16.5a). These tubes equalize air pressure on either side of the tympanic membrane (eardrum) by allowing air to move between the nasopharynx and the middle ear. Infections within the pharynx can move through the auditory tube into the middle ear, resulting in a middle ear infection (see Clinical View 16.9: “Otitis Media”). A collection of relatively small lymphatic nodules, called the tubal tonsils, is located near the pharyngeal opening of these tubes. The posterior nasopharynx wall also houses a single pharyngeal tonsil. When this tonsil is enlarged, clinicians refer to it as the adenoids (ad′ĕ-noydz; aden = gland, eidos = resemblance). Both the tubal and pharyngeal tonsils are composed of lymphatic tissue and help to prevent the spread of infections (see section 21.4c). Page 898 Oropharynx The middle pharyngeal region, called the oropharynx (ōr′ō-far′ingks), is immediately posterior to the oral cavity. The oropharynx extends from the level of the soft palate superiorly to the hyoid bone inferiorly. The palatine tonsils are located on lateral walls of the oropharynx, and the lingual tonsils are at the base of the tongue (and thus are in the anterior region of the oropharynx), providing defense against ingested or inhaled foreign materials (see figure 21.8). Laryngopharynx The inferior, narrowed region of the pharynx is the laryngopharynx (lă-ring′gō-far′ingks), which is located directly posterior to the larynx. It extends from the level of the hyoid bone and is continuous on its inferior end with both the larynx anteriorly and the esophagus posteriorly. Both the oropharynx and laryngopharynx serve as a common passageway for food and air. They are lined by a nonkeratinized stratified squamous epithelium to protect these regions of the pharynx from abrasion associated with swallowing food (see figure 23.2c). WHAT DID YOU LEARN? 6 What two regions of the pharynx contain tonsils? What is their purpose? 23.2d Larynx LEARNING OBJECTIVES 8. Identify and describe the structure and general functions of the larynx. 9. Explain how the larynx produces sounds. The larynx (lar′ingks), also called the voice box, is a somewhat cylindrical structure that averages about 4 centimeters (1.6 inches) in length ( figure 23.5). It is continuous superiorly with the laryngopharynx and inferiorly with the trachea. The superior opening from the laryngopharynx into the larynx is called the laryngeal (lă-rin′jē-ăl) inlet (laryngeal aperture, or laryngeal aditus). Functions of the Larynx The larynx has several major functions: Produces sound. Mucosa-covered ligaments within the larynx, called vocal folds, vibrate as air is passed over them during expiration. This vibration produces sound. Serves as a passageway for air. The vocal folds of the larynx typically are open or abducted to allow the passage of air. Prevents ingested materials from entering the respiratory tract. During swallowing, the laryngeal inlet is covered by the epiglottis to prevent ingested materials from entering the lower respiratory passageway. Assists in increasing pressure in the abdominal cavity. This occurs when the vocal folds are adducted and close off the rima glottidis (opening between the folds), and simultaneously abdominal muscles contract to increase abdominal pressure. This action is referred to as the Valsalva maneuver. You can experience the increase in abdominal pressure associated with the Valsalva maneuver by holding your breath while forcefully contracting your abdominal muscles. Page 899 Participates in both a sneeze and cough reflex. Both a sneeze and a cough result in an explosive blast of exhaled air. This occurs when the abdominal muscles contract forcefully and the vocal cords are initially closed and then open abruptly as the pressure increases in the thoracic cavity. Sneezing is a reflex (see sections 14.6a and 14.6b) initiated by irritants in the nasal cavity, whereas coughing is initiated by irritants in the trachea and bronchi. Both help remove irritants from the respiratory tract. INTEGRATE CONCEPT CONNECTION The Valsalva maneuver facilitates several physiologic processes, including the elimination of both urine from the urinary bladder (see section 24.8c) and feces from the gastrointestinal tract (see section 26.3d), and the expulsion of a baby during childbirth (see section 29.6d). Larynx Anatomy The larynx is shown from three views relative to the hyoid bone (see section 8.3) and trachea in figure 23.6. Observe that the larynx is supported by a framework of nine pieces of cartilage that are held in place by ligaments and muscles. The nine cartilages include the single thyroid, cricoid, and epiglottis cartilages, and the paired arytenoid, corniculate, and cuneiform cartilages. Figure 23.6 Larynx. The larynx shown in (a) an anterior view, (b) a posterior view, and (c) a posterior oblique view. It is composed of nine cartilages, various ligaments, and skeletal muscle. The nine cartilages, as well as extrinsic and intrinsic ligaments, form the flexible support of the larynx. Extrinsic muscles participate in moving the larynx, and intrinsic muscles function in sound production. APR Module 11: Respiratory: Dissection: Larynx: Anterior: Laryngeal Cartilages The thyroid cartilage is the largest laryngeal cartilage. Shaped like a shield, it forms the anterior and lateral walls of the larynx. The almost V-shaped anterior projection of the thyroid cartilage is called the laryngeal prominence (commonly referred to as the Adam’s apple). This protuberance is generally more prominent in males because (a) the laryngeal inlet is narrower in males (90 degrees) than in females (120 degrees), and (b) it enlarges at puberty due to testosterone-induced growth. The thyroid cartilage is attached to the lateral surface of the ring-shaped cricoid (krī′koyd; kridos = a ring) cartilage located inferior to the thyroid cartilage. The large, leaf-shaped epiglottis (ep-i-glot′is; epi = on, glottis = mouth of windpipe) is anchored to the inner aspect of the thyroid cartilage and projects posterosuperiorly (backward and upward) into the pharynx. It closes over the laryngeal inlet during swallowing ( figure 23.5b). The three smaller, paired cartilages, the arytenoid (ar-i-tē′noyd), corniculate (kōr′-ni-kū-lāt; corniculatus = horned), and cuneiform (kū′nē-i-fōrm; cuneus = wedge) cartilages, are located internally ( figure 23.6). All cartilages of the larynx, except the epiglottis, are composed of hyaline cartilage. The epiglottis, which opens and closes over the laryngeal inlet, is composed of the more flexible elastic cartilage (see section 5.2d). Laryngeal ligaments are classified as either extrinsic ligaments or intrinsic ligaments. Extrinsic ligaments attach to the external surface of laryngeal cartilages and extend to other structures that include the superiorly located hyoid bone and inferiorly located trachea. The intrinsic ligaments are located within the larynx and include both vocal ligaments and vestibular ligaments ( figure 23.7). The vocal ligaments are composed primarily of elastic connective tissue and extend anterior to posterior between the thyroid cartilage and the arytenoid cartilages. These ligaments are covered with a mucosa to form the vocal folds. Vocal folds also are called the true vocal cords because they vibrate to produce sound when air passes between them. They are distinctive from the surrounding tissue because they are avascular and white. The opening between these folds is called the rima glottidis (rī′mă glotī′dis; rima = slit). Together the vocal folds and the rima glottidis form the glottis. Figure 23.7 Vocal Folds. The vocal folds (true vocal cords) are elastic ligaments covered with a mucosa that extend between the thyroid and arytenoid cartilages. These folds surround the rima glottidis and are involved in sound production. Adducted (closed) and abducted (open) vocal folds are shown in (a) a superior view of the cartilages and ligaments only and (b) a diagrammatic laryngoscopic view of the coverings around these cartilages and ligaments. (c) A photo of a superolateral laryngoscopic view, showing the vocal folds and the rima glottidis, and the vestibular fold and rima vestibuli. (c) ©ISM/Medical Images Page 900 The vestibular (ves-tib′yu-lăr; vestibule = space at the entry of a canal) ligaments form the other intrinsic ligaments. These ligaments, which are superior to the vocal folds, extend between the thyroid cartilage to the arytenoid and corniculate cartilages. Together with the mucosa covering them, they form the vestibular folds. These folds also are called the false vocal cords because they have no function in sound production, but they protect the vocal folds and help in closing off the larynx (e.g., during swallowing). The opening between the vestibular folds is called the rima vestibuli. Skeletal muscles compose part of the larynx wall and are classified as either extrinsic or intrinsic muscles. The extrinsic muscles of the larynx attach to the thyroid cartilage on one end and extend either superiorly to attach to the hyoid bone (thyrohyoid; inferiorly to attach to the sternum (sternothyroid; see move the larynx during swallowing (see figure 23.6a) or figure 11.11). Extrinsic muscles sections 11.3d and 26.2c). The intrinsic muscles of the larynx are located within the larynx and attach to both the arytenoid and corniculate cartilages ( figure 23.6b, c). Contraction of the intrinsic muscles causes the arytenoid cartilages to pivot, resulting in abduction or adduction of the vocal folds, and a change in the dimension of the rima glottidis ( figure 23.7). The opening becomes narrower as the vocal folds are adducted and becomes wider if the vocal folds are abducted. They function in voice production. Sound Production Sound production (or phonation) originates as the vocal folds vibrate. This occurs when the intrinsic laryngeal muscles narrow the opening of the rima glottidis and air is forced past the vocal cords during an expiration. The characteristics of the sound include range, pitch, and loudness. The range of a voice (such as soprano or bass) is determined by the length and thickness of the vocal folds. Males generally have longer and thicker folds than do females, and thus males produce sounds that are in a lower range. Our vocal folds increase in length as we grow, which is why our voices become lower or deeper as we mature to adulthood. Pitch refers to the frequency of sound waves (see section 16.5b). Pitch is determined by the amount of tension or tautness on the vocal folds as regulated primarily by the intrinsic laryngeal muscles. Increasing the tension on the vocal folds causes the vocal folds to vibrate more when air passes by them and thus to produce a higher sound. Conversely, the less taut the vocal folds, the less they vibrate, and the lower the pitch of the sound. Loudness depends on the force of the air passing across the vocal cords. A lot of air forced through the rima glottidis produces a loud sound, whereas a little air produces a soft sound. When you whisper, only the most posterior portion of the rima glottidis is open, and the vocal folds do not vibrate. Because the vocal folds are not vibrating, the whispered sounds are all of the same pitch. Speech (or the articulation or enunciation of words) also requires the participation of the spaces in the pharynx, nasal and oral cavities, and paranasal sinuses, which serve as resonating chambers for sound, and the structures of the lips, teeth, and tongue that help form different sounds. Young children tend to have high, nasal-like voices because their sinuses are not yet well developed, so they lack large resonating chambers. When you hold your nose and speak, your voice sounds quite different because air doesn’t pass through the nasal cavity. Page 901 INTEGRATE CLINICAL VIEW 23.4 Laryngitis Laryngitis (lar-in-jĪ΄tis) is an inflammation of the larynx that may extend to its surrounding structures. Viral or bacterial infection (see section 22.1) is the number one cause of laryngitis. Less frequently, laryngitis follows overuse of the voice, such as yelling for several hours at a sporting match. Symptoms include hoarse voice, sore throat, and sometimes fever. Severe cases can produce inflammation and swelling extending to the epiglottis. Children's airways are proportionately smaller, and a swollen and inflamed epiglottis (called epiglottitis) may lead to sudden airway obstruction and become a medical emergency. A laryngoscopic view shows the inflamed, reddened vocal folds characteristic of laryngitis. ©C. Richard Stasney, M.D. WHAT DID YOU LEARN? 7 How does the larynx assist in increasing abdominal pressure? 8 What are the three unpaired cartilages in the larynx? 9 What are the structural and functional differences between the vocal folds and vestibular folds?