Respiratory System Anatomy PDF

2568T_c23_874-920.qxd 1/26/08 8:48 PM Page 875 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 875 RESPIRATORY SYSTEM ANATOMY...

2568T_c23_874-920.qxd 1/26/08 8:48 PM Page 875 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 875 RESPIRATORY SYSTEM ANATOMY CLINICAL CONNECTION Rhinoplasty  OBJECTIVES Rhinoplasty (RĪ-nō-plas-tē; -plasty  to mold or to shape), commonly Describe the anatomy and histology of the nose, pharynx, called a “nose job,” is a surgical procedure in which the shape of the larynx, trachea, bronchi, and lungs. external nose is altered. Although rhinoplasty is often done for cosmetic Identify the functions of each respiratory system structure. reasons, it is sometimes performed to repair a fractured nose or a devi- The respiratory system consists of the nose, pharynx (throat), ated nasal septum. In the procedure, both local and general anesthetics larynx (voice box), trachea (windpipe), bronchi, and lungs are given. Instruments are then inserted through the nostrils, the nasal cartilage is reshaped, and the nasal bones are fractured and reposi- (Figure 23.1). Its parts can be classified according to either tioned to achieve the desired shape. An internal packing and splint are structure or function. Structurally, the respiratory system con- inserted to keep the nose in the desired position as it heals. sists of two parts: (1) The upper respiratory system includes the nose, pharynx, and associated structures. (2) The lower respiratory system includes the larynx, trachea, bronchi, and The internal nose is a large cavity beyond the nasal vestibule lungs. Functionally, the respiratory system also consists of two in the anterior aspect of the skull that lies inferior to the nasal parts: (1) The conducting zone consists of a series of intercon- bone and superior to the mouth; it is lined with muscle and mu- necting cavities and tubes both outside and within the lungs. cous membrane. Anteriorly, the internal nose merges with the These include the nose, pharynx, larynx, trachea, bronchi, bron- external nose, and posteriorly it communicates with the pharynx chioles, and terminal bronchioles; their function is to filter, through two openings called the internal nares or choanae (kō- warm, and moisten air and conduct it into the lungs. (2) The res- Ā -nē) (see Figure 23.2b). Ducts from the paranasal sinuses piratory zone consists of tissues within the lungs where gas ex- (which drain mucus) and the nasolacrimal ducts (which drain change occurs. These include the respiratory bronchioles, alveo- tears) also open into the internal nose. Recall from Chapter 7 lar ducts, alveolar sacs, and alveoli; they are the main sites of that the paranasal sinuses are cavities in certain cranial and gas exchange between air and blood. facial bones lined with mucous membranes that are The branch of medicine that deals with the diagnosis and continuous with the lining of the nasal cavity. Skull bones con- treatment of diseases of the ears, nose, and throat (ENT) is taining the paranasal sinuses are the frontal, sphenoid, ethmoid, called otorhinolaryngology (ō-tō-rı̄-nō-lar-in-GOL-ō-jē; oto- and maxillae. Besides producing mucus, the paranasal sinuses  ear; rhino-  nose; laryngo-  voice box; -logy  study of). serve as resonating chambers for sound as we speak or sing. The A pulmonologist is a specialist in the diagnosis and treatment of lateral walls of the internal nose are formed by the ethmoid, diseases of the lungs. maxillae, lacrimal, palatine, and inferior nasal conchae bones (see Figure 7.9 on page 210); the ethmoid bone also forms the roof. The palatine bones and palatine processes of the maxillae, Nose which together constitute the hard palate, form the floor of the The nose can be divided into external and internal portions. internal nose. The external nose is the portion of the nose visible on the face The space within the internal nose is called the nasal cavity. and consists of a supporting framework of bone and hyaline The anterior portion of the nasal cavity just inside the nostrils, cartilage covered with muscle and skin and lined by a mucous called the nasal vestibule, is surrounded by cartilage; the supe- membrane. The frontal bone, nasal bones, and maxillae form rior part of the nasal cavity is surrounded by bone. A vertical the bony framework of the external nose (Figure 23.2a on page partition, the nasal septum, divides the nasal cavity into right 877). The cartilaginous framework of the external nose con- and left sides. The anterior portion of the nasal septum consists sists of the septal nasal cartilage, which forms the anterior primarily of hyaline cartilage; the remainder is formed by the portion of the nasal septum; the lateral nasal cartilages inferior vomer, perpendicular plate of the ethmoid, maxillae, and pala- to the nasal bones; and the alar cartilages, which form a por- tine bones (see Figure 7.11 on page 213). tion of the walls of the nostrils. Because it consists of pliable When air enters the nostrils, it passes first through the hyaline cartilage, the cartilaginous framework of the external vestibule, which is lined by skin containing coarse hairs that fil- nose is somewhat flexible. On the undersurface of the external ter out large dust particles. Three shelves formed by projections nose are two openings called the external nares (NĀ -rez; sin- of the superior, middle, and inferior nasal conchae extend out of gular is naris) or nostrils. Figure 23.3 on page 878 shows the each lateral wall of the nasal cavity. The conchae, almost reach- surface anatomy of the nose. ing the nasal septum, subdivide each side of the nasal cavity into The interior structures of the external nose have three a series of groovelike passageways—the superior, middle, and functions: (1) warming, moistening, and filtering incoming air; inferior meatuses (mē-Ā -tus-ēz  openings or passages; sin- (2) detecting olfactory stimuli; and (3) modifying speech gular is meatus). Mucous membrane lines the cavity and its vibrations as they pass through the large, hollow resonating shelves. The arrangement of conchae and meatuses increases chambers. Resonance refers to prolonging, amplifying, or modi- surface area in the internal nose and prevents dehydration by fying a sound by vibration. trapping water droplets during exhalation. 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 876 Team B venus:JWQY057:ch23: Figure 23.1 Structures of the respiratory system. The upper respiratory system includes the nose, pharynx, and associated structures; the lower respiratory system includes the larynx, trachea, bronchi, and lungs. Nose Nasal cavity Oral cavity Pharynx Larynx Trachea Right primary Functions bronchus 1. Provides for gas exchange—intake of O2 Lungs for delivery to body cells and elimination of CO2 produced by body cells. 2. Helps regulate blood pH. 3. Contains receptors for the sense of smell, filters inspired air, produces vocal sounds (phonation), and excretes small amounts of water and heat. (a) Anterior view showing organs of respiration Larynx Right common carotid artery Thyroid gland Trachea Subclavian artery Right subclavian artery Phrenic nerve Brachiocephalic artery Left common carotid artery Superior vena cava Arch of aorta 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 ? Which structures are part of the conducting zone of the respiratory system? 876 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 877 Team B venus:JWQY057:ch23: Figure 23.2 Respiratory structures in the head and neck. (See Tortora, A Photographic Atlas of the Human Body, Second Edition, Figures 11.2 and 11.3.) As air passes through the nose, it is warmed, filtered, moistened, and olfaction occurs. Bony framework: Frontal bone Nasal bones Maxilla Cartilaginous framework: Lateral nasal cartilages Septal nasal cartilage Alar cartilage Dense fibrous connective and adipose tissue (a) Anterolateral view of external portion of nose showing cartilaginous and bony framework Sagittal Superior plane Middle Nasal meatuses Frontal sinus Inferior Frontal bone Olfactory epithelium Sphenoid 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 (hypopharynx) Ventricular fold (false vocal cord) Vocal fold (true vocal cord) Larynx Esophagus Nasopharynx Thyroid cartilage Oropharynx Trachea Cricoid cartilage Thyroid gland Laryngopharynx Regions of the pharynx (b) Sagittal section of the left side of the head and neck showing the location of respiratory structures F I G U R E 23.2 CO N T I N U E S 877 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 878 Team B venus:JWQY057:ch23: 878 CHAPTER 23 THE RESPIRATORY SYSTEM F I G U R E 23.2 CO N T I N U E D Periorbital fat Frontal plane Ethmoidal cell Eyeball View Superior nasal concha Middle nasal concha Nasal septum: Perpendicular plate of ethmoid Vomer Inferior nasal concha Maxillary sinus Hard palate (c) Frontal section showing conchae ? What is the path taken by air molecules into and through the nose? Figure 23.3 Surface anatomy of the nose. The olfactory receptors lie in a region of the membrane lining the superior nasal conchae and adjacent septum called the The external nose has a cartilaginous framework olfactory epithelium. Inferior to the olfactory epithelium, the and a bony framework. mucous membrane contains capillaries and pseudostratified ciliated columnar epithelium with many goblet cells. As inhaled air whirls around the conchae and meatuses, it is warmed by blood in the capillaries. Mucus secreted by the goblet cells moistens the air and traps dust particles. Drainage from the nasolacrimal ducts also helps moisten the air, and is sometimes assisted by secretions from the paranasal sinuses. The cilia move 1 the mucus and trapped dust particles toward the pharynx, at 3 which point they can be swallowed or spit out, thus removing the particles from the respiratory tract. 2 4  CHECKPOINT 1. What functions do the respiratory and cardiovascular systems have in common? 2. What structural and functional features are different in the upper and lower respiratory systems? Which are the same? 3. Compare the structure and functions of the external nose and the internal nose. Anterior view 1. Root: Superior attachment of the nose to the frontal bone Pharynx 2. Apex: Tip of nose 3. Bridge: Bony framework of nose formed by nasal bones The pharynx (FAIR-inks), or throat, is a funnel-shaped tube 4. External naris: Nostril; external opening into nasal cavity about 13 cm (5 in.) long that starts at the internal nares and ? Which part of the nose is attached to the frontal bone? extends to the level of the cricoid cartilage, the most inferior cartilage of the larynx (voice box) (see Figure 23.2b). The phar- 2568T_c23_874-920.qxd 2/2/08 8:20 AM Page 879 epg venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 879 ynx lies just posterior to the nasal and oral cavities, superior to Larynx the larynx, and just anterior to the cervical vertebrae. Its wall is composed of skeletal muscles and is lined with a mucous The larynx (LAIR-inks), or voice box, is a short passageway membrane. Contraction of the skeletal muscles assists in degluti- that connects the laryngopharynx with the trachea. It lies in the tion (swallowing). The pharynx functions as a passageway for midline of the neck anterior to the esophagus and the fourth air and food, provides a resonating chamber for speech sounds, through sixth cervical vertebrae (C4–C6). and houses the tonsils, which participate in immunological reac- The wall of the larynx is composed of nine pieces of cartilage tions against foreign invaders. (Figure 23.4). Three occur singly (thyroid cartilage, epiglottis, and The pharynx can be divided into three anatomical regions: (1) cricoid cartilage), and three occur in pairs (arytenoid, cuneiform, nasopharynx, (2) oropharynx, and (3) laryngopharynx. (See the and corniculate cartilages). Of the paired cartilages, the arytenoid lower orientation diagram in Figure 23.2b.) The muscles of the cartilages are the most important because they influence changes entire pharynx are arranged in two layers, an outer circular layer in position and tension of the vocal folds (true vocal cords for and an inner longitudinal layer. speech). The extrinsic muscles of the larynx connect the cartilages The superior portion of the pharynx, called the nasopharynx, to other structures in the throat; the intrinsic muscles connect the lies posterior to the nasal cavity and extends to the soft palate. cartilages to one another. The soft palate, which forms the posterior portion of the roof of The thyroid cartilage (Adam’s apple) consists of two fused the mouth, is an arch-shaped muscular partition between the na- plates of hyaline cartilage that form the anterior wall of the lar- sopharynx and oropharynx that is lined by mucous membrane. ynx and give it a triangular shape. It is present in both males and There are five openings in its wall: two internal nares, two open- females but is usually larger in males due to the influence of ings that lead into the auditory (pharyngotympanic) tubes (com- male sex hormones on its growth during puberty. The ligament monly known as the eustachian tubes), and the opening into the that connects the thyroid cartilage to the hyoid bone is called the oropharynx. The posterior wall also contains the pharyngeal thyrohyoid membrane. tonsil (adenoid). Through the internal nares, the nasopharynx The epiglottis (epi-  over; glottis  tongue) is a large, leaf- receives air from the nasal cavity along with packages of dust- shaped piece of elastic cartilage that is covered with epithelium laden mucus. The nasopharynx is lined with pseudostratified cil- (see also Figure 23.2b). The “stem” of the epiglottis is the ta- iated columnar epithelium, and the cilia move the mucus down pered inferior portion that is attached to the anterior rim of toward the most inferior part of the pharynx. The nasopharynx the thyroid cartilage and hyoid bone. The broad superior “leaf” also exchanges small amounts of air with the auditory tubes to portion of the epiglottis is unattached and is free to move up and equalize air pressure between the pharynx and the middle ear. down like a trap door. During swallowing, the pharynx and The intermediate portion of the pharynx, the oropharynx, larynx rise. Elevation of the pharynx widens it to receive food or lies posterior to the oral cavity and extends from the soft palate drink; elevation of the larynx causes the epiglottis to move down inferiorly to the level of the hyoid bone. It has only one opening and form a lid over the glottis, closing it off. The glottis consists into it, the fauces (FAW-sēz  throat), the opening from the of a pair of folds of mucous membrane, the vocal folds (true mouth. This portion of the pharynx has both respiratory and vocal cords) in the larynx, and the space between them called digestive functions, serving as a common passageway for air, the rima glottidis (RĪ -ma GLOT-ti-dis). The closing of the food, and drink. Because the oropharynx is subject to abrasion larynx in this way during swallowing routes liquids and foods by food particles, it is lined with nonkeratinized stratified squa- into the esophagus and keeps them out of the larynx and mous epithelium. Two pairs of tonsils, the palatine and lingual airways. When small particles of dust, smoke, food, or liquids tonsils, are found in the oropharynx. pass into the larynx, a cough reflex occurs, usually expelling The inferior portion of the pharynx, the laryngopharynx (la- the material. rin-gō-FAIR-inks), or hypopharynx, begins at the level of the The cricoid cartilage (KRĪ -koyd  ringlike) is a ring of hya- hyoid bone. At its inferior end it opens into the esophagus (food line cartilage that forms the inferior wall of the larynx. It is at- tube) posteriorly and the larynx (voice box) anteriorly. Like the tached to the first ring of cartilage of the trachea by the oropharynx, the laryngopharynx is both a respiratory and a di- cricotracheal ligament. The thyroid cartilage is connected gestive pathway and is lined by nonkeratinized stratified squa- to the cricoid cartilage by the cricothyroid ligament. The mous epithelium. cricoid cartilage is the landmark for making an emergency air- way called a tracheotomy (see page 882). CLINICAL CONNECTION Tonsillectomy The paired arytenoid cartilages (ar-i-TĒ-noyd  ladlelike) are triangular pieces of mostly hyaline cartilage located at the Tonsillectomy (ton-si-LEK-to- -me-; -ektome  excision) is surgical removal posterior, superior border of the cricoid cartilage. They form of the tonsils. The procedure is usually performed under general anes- synovial joints with the cricoid cartilage and have a wide range thesia on an outpatient basis. Tonsillectomies are performed in individu- of mobility. - als who have frequent tonsillitis (ton-si-LI-tis), that is, inflammation of the The paired corniculate cartilages (kor-NIK-u--la-t  shaped tonsils; tonsils that develop an abcess or tumor; or when the tonsils like a small horn), horn-shaped pieces of elastic cartilage, are obstruct breathing during sleep. located at the apex of each arytenoid cartilage. The paired 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 880 Team B venus:JWQY057:ch23: 880 CHAPTER 23 THE RESPIRATORY SYSTEM Figure 23.4 Larynx. (See Tortora, A Photographic Atlas of the Human Body, Second Edition, Figures 11.5 and 11.6.) The larynx is composed of nine pieces of cartilage. Epiglottis Hyoid bone Thyrohyoid membrane Epiglottis: Leaf Stem Corniculate cartilage Thyroid cartilage (Adam’s apple) Larynx Thyroid Arytenoid cartilage gland 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 Ventricular fold (false vocal cord) Arytenoid cartilage Thyroid cartilage Vocal fold (true vocal cord) Cricoid cartilage Cricothyroid ligament Cricotracheal ligament Tracheal cartilage (c) Sagittal section ? How does the epiglottis prevent aspiration of foods and liquids? - cuneiform cartilages (KU-ne--i-form  wedge-shaped), club- epithelium consisting of ciliated columnar cells, goblet cells, and shaped elastic cartilages anterior to the corniculate cartilages, basal cells. The mucus produced by the goblet cells helps trap support the vocal folds and lateral aspects of the epiglottis. dust not removed in the upper passages. The cilia in the upper The lining of the larynx superior to the vocal folds is nonker- respiratory tract move mucus and trapped particles down toward atinized stratified squamous epithelium. The lining of the larynx the pharynx; the cilia in the lower respiratory tract move them inferior to the vocal folds is pseudostratified ciliated columnar up toward the pharynx. 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 881 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 881 The Structures of Voice Production sounds (phonation) by setting up sound waves in the column of air in the pharynx, nose, and mouth. The greater the pressure of The mucous membrane of the larynx forms two pairs of air, the louder the sound. folds (Figure 23.4c): a superior pair called the ventricu- When the intrinsic muscles of the larynx contract, they lar folds (false vocal cords) and an inferior pair called the vocal pull on the arytenoid cartilages, which causes them to pivot and folds (true vocal cords). The space between the ventricu- slide. Contraction of the posterior cricoarytenoid muscles, for lar folds is known as the rima vestibuli. The laryngeal sinus example, moves the vocal folds apart (abduction), thereby open- (ventricle) is a lateral expansion of the middle portion of the ing the rima glottidis (Figure 23.5a). By contrast, contraction of laryngeal cavity inferior to the ventricular folds and superior to the lateral cricoarytenoid muscles moves the vocal folds together the vocal folds (see Figure 23.2b). (adduction), thereby closing the rima glottidis (Figure 23.5b). When the ventricular folds are brought together, they function Other intrinsic muscles can elongate (and place tension on) or in holding the breath against pressure in the thoracic cavity, such shorten (and relax) the vocal folds. as might occur when you strain to lift a heavy object. Deep to Pitch is controlled by the tension on the vocal folds. If they the mucous membrane of the vocal folds, which is lined by are pulled taut by the muscles, they vibrate more rapidly, and a nonkeratinized stratified squamous epithelium, bands of elastic higher pitch results. Decreasing the muscular tension on the ligaments are stretched between pieces of rigid cartilage like the vocal folds causes them to vibrate more slowly and produce strings on a guitar. Intrinsic laryngeal muscles attach to both the lower-pitch sounds. Due to the influence of androgens (male sex rigid cartilage and the vocal folds. When the muscles contract, hormones), vocal folds are usually thicker and longer in males they pull the elastic ligaments tight and stretch the vocal folds than in females, and therefore they vibrate more slowly. This is out into the airways so that the rima glottidis is narrowed. If air why a man’s voice generally has a lower range of pitch than that is directed against the vocal folds, they vibrate and produce of a woman. Figure 23.5 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 (true vocal cords) Vocal ligament Rima glottidis Ventricular folds (false vocal cords) 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) Lateral cricoarytenoid muscle (b) Movement of vocal folds together (adduction) F I G U R E 23.5 CO N T I N U E S 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 882 Team B venus:JWQY057:ch23: 882 CHAPTER 23 THE RESPIRATORY SYSTEM F I G U R E 23.5 CO N T I N U E D Epiglottis View Vocal folds (true vocal chords) Rima Larynx glottidis Ventricular Cuneiform folds (false cartilage vocal chords) Corniculate cartilage (c) Superior view ? What is the main function of the vocal folds? Sound originates from the vibration of the vocal folds, but The layers of the tracheal wall, from deep to superficial, other structures are necessary for converting the sound into are the (1) mucosa, (2) submucosa, (3) hyaline cartilage, and recognizable speech. The pharynx, mouth, nasal cavity, and (4) adventitia (composed of areolar connective tissue). The paranasal sinuses all act as resonating chambers that give the mucosa of the trachea consists of an epithelial layer of pseudo- voice its human and individual quality. We produce the vowel stratified ciliated columnar epithelium and an underlying layer sounds by constricting and relaxing the muscles in the wall of of lamina propria that contains elastic and reticular fibers. the pharynx. Muscles of the face, tongue, and lips help us enun- Pseudostratified ciliated columnar epithelium consists of ciliated ciate words. columnar cells and goblet cells that reach the luminal surface, Whispering is accomplished by closing all but the posterior plus basal cells that do not (see Table 4.1E on page 117); it pro- portion of the rima glottidis. Because the vocal folds do not vides the same protection against dust as the membrane lining vibrate during whispering, there is no pitch to this form of the nasal cavity and larynx. The submucosa consists of areolar speech. However, we can still produce intelligible speech while connective tissue that contains seromucous glands and their ducts. whispering by changing the shape of the oral cavity as we The 16–20 incomplete, horizontal rings of hyaline cartilage enunciate. As the size of the oral cavity changes, its resonance resemble the letter C, are stacked one above another, and are qualities change, which imparts a vowel-like pitch to the air as it connected together by dense connective tissue. They may be felt rushes toward the lips. through the skin inferior to the larynx. The open part of each C-shaped cartilage ring faces posteriorly toward the esophagus (Figure 23.6) and is spanned by a fibromuscular membrane. CLINICAL CONNECTION Laryngitis and Cancer Within this membrane are transverse smooth muscle fibers, of the Larynx called the trachealis muscle, and elastic connective tissue that Laryngitis is an inflammation of the larynx that is most often caused allow the diameter of the trachea to change subtly during inhala- by a respiratory infection or irritants such as cigarette smoke. tion and exhalation, which is important in maintaining efficient Inflammation of the vocal folds causes hoarseness or loss of voice by airflow. The solid C-shaped cartilage rings provide a semirigid interfering with the contraction of the folds or by causing them to swell support so that the tracheal wall does not collapse inward (espe- to the point where they cannot vibrate freely. Many long-term smokers cially during inhalation) and obstruct the air passageway. The acquire a permanent hoarseness from the damage done by chronic in- adventitia of the trachea consists of areolar connective tissue that flammation. Cancer of the larynx is found almost exclusively in individ- joins the trachea to surrounding tissues. uals who smoke. The condition is characterized by hoarseness, pain on swallowing, or pain radiating to an ear. Treatment consists of radiation therapy and/or surgery. CLINICAL CONNECTION Tracheotomy and Intubation Trachea Several conditions may block airflow by obstructing the trachea. For ex- The trachea (TRĀ-kē-a  sturdy), or windpipe, is a tubular ample, the rings of cartilage that support the trachea may collapse due passageway for air that is about 12 cm (5 in.) long and 2.5 cm to a crushing injury to the chest, inflammation of the mucous mem- brane may cause it to swell so much that the airway closes, vomit or a (1 in.) in diameter. It is located anterior to the esophagus foreign object may be aspirated into it, or a cancerous tumor may pro- (Figure 23.6) and extends from the larynx to the superior border trude into the airway. Two methods are used to reestablish airflow past of the fifth thoracic vertebra (T5), where it divides into right and a tracheal obstruction. If the obstruction is superior to the level of the left primary bronchi (see Figure 23.7). 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 883 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 883 Figure 23.6 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 Cartilage of trachea Right lateral lobe of thyroid gland Left lateral lobe of thyroid gland Fibromuscular membrane of trachea (contains trachealis muscle) Esophagus POSTERIOR Superior view of transverse section of thyroid gland, trachea, and esophagus ? What is the benefit of not having complete rings of tracheal cartilage between the trachea and the esophagus? projection of the last tracheal cartilage. The mucous membrane larynx, a tracheotomy (trā-kē-O-tō-mē; -tome  cutting), an operation of the carina is one of the most sensitive areas of the entire to make an opening into the trachea, may be performed. In this proce- larynx and trachea for triggering a cough reflex. Widening and dure, also called a tracheostomy, a skin incision is followed by a short longitudinal incision into the trachea inferior to the cricoid cartilage. distortion of the carina is a serious sign because it usually indi- The patient can then breathe through a metal or plastic tracheal tube in- cates a carcinoma of the lymph nodes around the region where serted through the incision. The second method is intubation, in which the trachea divides. a tube is inserted into the mouth or nose and passed inferiorly through On entering the lungs, the primary bronchi divide to form the larynx and trachea. The firm wall of the tube pushes aside any flexible smaller bronchi—the secondary (lobar) bronchi, one for each obstruction, and the lumen of the tube provides a passageway for air; any lobe of the lung. (The right lung has three lobes; the left lung mucus clogging the trachea can be suctioned out through the tube. has two.) The secondary bronchi continue to branch, forming still smaller bronchi, called tertiary (segmental) bronchi, that divide into bronchioles. Bronchioles in turn branch repeatedly, and the smallest ones branch into even smaller tubes called Bronchi terminal bronchioles. This extensive branching from the trachea resembles an inverted tree and is commonly referred to At the superior border of the fifth thoracic vertebra, the trachea as the bronchial tree. divides into a right primary bronchus (BRON-kus  wind- As the branching becomes more extensive in the bronchial pipe), which goes into the right lung, and a left primary tree, several structural changes may be noted. bronchus, which goes into the left lung (Figure 23.7). The right primary bronchus is more vertical, shorter, and wider than the 1. The mucous membrane in the bronchial tree changes from left. As a result, an aspirated object is more likely to enter and pseudostratified ciliated columnar epithelium in the primary lodge in the right primary bronchus than the left. Like the bronchi, secondary bronchi, and tertiary bronchi to ciliated trachea, the primary bronchi (BRON-kē) contain incomplete simple columnar epithelium with some goblet cells in larger rings of cartilage and are lined by pseudostratified ciliated bronchioles, to mostly ciliated simple cuboidal epithelium with columnar epithelium. no goblet cells in smaller bronchioles, to mostly nonciliated At the point where the trachea divides into right and left simple cuboidal epithelium in terminal bronchioles. (In regions primary bronchi an internal ridge called the carina (ka-RĪ -na  where simple nonciliated cuboidal epithelium is present, inhaled keel of a boat) is formed by a posterior and somewhat inferior particles are removed by macrophages.) 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 884 Team B venus:JWQY057:ch23: 884 CHAPTER 23 THE RESPIRATORY SYSTEM Figure 23.7 Branching of airways from the trachea: the bronchial tree. (See Tortora, A Photographic Atlas of the Human Body, Second Edition, Figure 11.8.) The bronchial tree begins at the trachea and ends at the terminal bronchioles. BRANCHING OF BRONCHIAL TREE Larynx Trachea Trachea Primary bronchi Secondary bronchi Tertiary bronchi Visceral pleura Bronchioles Parietal pleura Terminal bronchioles Pleural cavity Location of carina Right primary bronchus Left primary bronchus Right secondary Left secondary bronchus bronchus Left tertiary bronchus Right tertiary bronchus Left bronchiole Right bronchiole Left terminal bronchiole Right terminal bronchiole Diaphragm Anterior view ? How many lobes and secondary bronchi are present in each lung? 2. Plates of cartilage gradually replace the incomplete rings of alveoli more quickly, lung ventilation improves. The parasympa- cartilage in primary bronchi and finally disappear in the distal thetic division of the ANS and mediators of allergic reactions bronchioles. such as histamine have the opposite effect, causing contraction 3. As the amount of cartilage decreases, the amount of smooth of bronchiolar smooth muscle, which results in constriction of muscle increases. Smooth muscle encircles the lumen in spiral distal bronchioles. bands. Because there is no supporting cartilage, however, muscle  CHECKPOINT spasms can close off the airways. This is what happens during an 4. List the roles of each of the three anatomical regions of asthma attack, which can be a life-threatening situation. the pharynx in respiration. During exercise, activity in the sympathetic division of the 5. How does the larynx function in respiration and voice production? autonomic nervous system (ANS) increases and the adrenal 6. Describe the location, structure, and function of the medulla releases the hormones epinephrine and norepinephrine; trachea. both of these events cause relaxation of smooth muscle in the 7. Describe the structure of the bronchial tree. bronchioles, which dilates the airways. Because air reaches the 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 885 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 885 Lungs CLINICAL CONNECTION Pneumothorax and The lungs ( lightweights, because they float) are paired Hemothorax cone-shaped organs in the thoracic cavity. They are separated In certain conditions, the pleural cavities may fill with air (pneumotho- from each other by the heart and other structures in the rax; pneumo-  air or breath), blood (hemothorax), or pus. Air in the mediastinum, which divides the thoracic cavity into two pleural cavities, most commonly introduced in a surgical opening of the anatomically distinct chambers. As a result, if trauma causes chest or as a result of a stab or gunshot wound, may cause the lungs to one lung to collapse, the other may remain expanded. Each lung collapse. This collapse of a part of a lung, or rarely an entire lung, is is enclosed and protected by a double-layered serous membrane called atelectasis (at-e-LEK-ta-sis; ateles-  incomplete; -ectasis-  called the pleural membrane (PLOOR-al; pleur-  side). expansion). The goal of treatment is the evacuation of air (or blood) The superficial layer, called the parietal pleura, lines the wall from the pleural space, which allows the lung to reinflate. A small pneu- of the thoracic cavity; the deep layer, the visceral pleura, covers mothorax may resolve on its own, but it is often necessary to insert a the lungs themselves (Figure 23.8). Between the visceral and chest tube to assist in evacuation. parietal pleurae is a small space, the pleural cavity, which contains a small amount of lubricating fluid secreted by the membranes. This pleural fluid reduces friction between the The lungs extend from the diaphragm to just slightly superior membranes, allowing them to slide easily over one another dur- to the clavicles and lie against the ribs anteriorly and posteriorly ing breathing. Pleural fluid also causes the two membranes to (Figure 23.9a). The broad inferior portion of the lung, the base, adhere to one another just as a film of water causes two glass mi- is concave and fits over the convex area of the diaphragm. The croscope slides to stick together, a phenomenon called surface narrow superior portion of the lung is the apex. The surface of tension. Separate pleural cavities surround the left and right the lung lying against the ribs, the costal surface, matches the lungs. Inflammation of the pleural membrane, called pleurisy or rounded curvature of the ribs. The mediastinal (medial) surface pleuritis, may in its early stages cause pain due to friction be- of each lung contains a region, the hilum, through which tween the parietal and visceral layers of the pleura. If the inflam- bronchi, pulmonary blood vessels, lymphatic vessels, and nerves mation persists, excess fluid accumulates in the pleural space, a enter and exit (Figure 23.9e). These structures are held together condition known as pleural effusion. by the pleura and connective tissue and constitute the root of the Figure 23.8 Relationship of the pleural membranes to the lungs. The parietal pleura lines the thoracic cavity, and the visceral pleura covers the lungs. Transverse Sternum plane Left lung Visceral pleura Ascending aorta Superior vena cava Pulmonary arteries Parietal pleura Pulmonary vein View Right lung Esophagus Pleural cavity Thoracic aorta Body of T4 Spinal cord LATERAL MEDIAL POSTERIOR Inferior view of a transverse section through the thoracic cavity showing the pleural cavity and pleural membranes ? What type of membrane is the pleural membrane? 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 886 Team B venus:JWQY057:ch23: 886 CHAPTER 23 THE RESPIRATORY SYSTEM Figure 23.9 Surface anatomy of the lungs. (See Tortora, First rib A Photographic Atlas of the Human Body, Second Edition, Figures 11.12 and 11.14.) Apex of lung The oblique fissure divides the left lung into two lobes. The oblique and horizontal fissures Left lung divide the right lung into three lobes. Base of lung Pleural cavity Pleura (a) Anterior view of lungs and pleurae in thorax Apex Superior lobe View (b) View (c) ANTERIOR Horizontal fissure Oblique 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 Hilus 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 ? Why are the right and left lungs slightly different in size and shape? lung. Medially, the left lung also contains a concavity, the car- what shorter than the left lung because the diaphragm is higher diac notch, in which the heart lies. Due to the space occupied by on the right side, accommodating the liver that lies inferior to it. the heart, the left lung is about 10% smaller than the right lung. The lungs almost fill the thorax (Figure 23.9a). The apex of Although the right lung is thicker and broader, it is also some- the lungs lies superior to the medial third of the clavicles and is 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 887 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 887 the only area that can be palpated. The anterior, lateral, and Each lobe receives its own secondary (lobar) bronchus. Thus, posterior surfaces of the lungs lie against the ribs. The base of the right primary bronchus gives rise to three secondary (lobar) the lungs extends from the sixth costal cartilage anteriorly to the bronchi called the superior, middle, and inferior secondary spinous process of the tenth thoracic vertebra posteriorly. The (lobar) bronchi, and the left primary bronchus gives rise to su- pleura extends about 5 cm (2 in.) below the base from the sixth perior and inferior secondary (lobar) bronchi. Within the costal cartilage anteriorly to the twelfth rib posteriorly. Thus, the lung, the secondary bronchi give rise to the tertiary (segmental) lungs do not completely fill the pleural cavity in this area. bronchi, which are constant in both origin and distribution— Removal of excessive fluid in the pleural cavity can be there are 10 tertiary bronchi in each lung. The segment of lung accomplished without injuring lung tissue by inserting a needle tissue that each tertiary bronchus supplies is called a bron- anteriorly through the seventh intercostal space, a procedure chopulmonary segment. Bronchial and pulmonary disorders called thoracentesis (thor-a-sen-TE Ē -sis; -centesis  puncture). (such as tumors or abscesses) that are localized in a bronchopul- The needle is passed along the superior border of the lower rib monary segment may be surgically removed without seriously to avoid damage to the intercostal nerves and blood vessels. disrupting the surrounding lung tissue. Inferior to the seventh intercostal space there is danger of Each bronchopulmonary segment of the lungs has many penetrating the diaphragm. small compartments called lobules; each lobule is wrapped in elastic connective tissue and contains a lymphatic vessel, an Lobes, Fissures, and Lobules arteriole, a venule, and a branch from a terminal bronchiole One or two fissures divide each lung into lobes (Figure (Figure 23.10a). Terminal bronchioles subdivide into micro- 23.9b–e). Both lungs have an oblique fissure, which extends in- scopic branches called respiratory bronchioles (Figure 23.10b). feriorly and anteriorly; the right lung also has a horizontal As the respiratory bronchioles penetrate more deeply into the fissure. The oblique fissure in the left lung separates the supe- lungs, the epithelial lining changes from simple cuboidal to sim- rior lobe from the inferior lobe. In the right lung, the superior ple squamous. Respiratory bronchioles in turn subdivide into part of the oblique fissure separates the superior lobe from the several (2–11) alveolar ducts. The respiratory passages from the inferior lobe; the inferior part of the oblique fissure separates the trachea to the alveolar ducts contain about 25 orders of branch- inferior lobe from the middle lobe, which is bordered superiorly ing; branching from the trachea into primary bronchi is called by the horizontal fissure. first-order branching, from primary bronchi into secondary Figure 23.10 Microscopic anatomy of a lobule of the lungs. Alveolar sacs consist of two or more alveoli that share a common opening. Terminal bronchiole Terminal bronchiole Pulmonary Pulmonary arteriole venule Lymphatic Blood vessel vessel Elastic Respiratory connective bronchiole Respiratory tissue bronchiole Alveolar ducts Alveolar ducts Alveoli Pulmonary capillary Alveolar Alveolar Visceral sac sacs pleura Alveoli Visceral pleura LM about 30x (a) Diagram of a portion of a lobule of the lung (b) Lung lobule ? What types of cells make up the wall of an alveolus? 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 888 Team B venus:JWQY057:ch23: 888 CHAPTER 23 THE RESPIRATORY SYSTEM bronchi is called second-order branching, and so on down to the is surfactant (sur-FAK-tant), a complex mixture of phospho- alveolar ducts. lipids and lipoproteins. Surfactant lowers the surface tension of alveolar fluid, which reduces the tendency of alveoli to collapse Alveoli (described later). Around the circumference of the alveolar ducts are numerous Associated with the alveolar wall are alveolar macrophages alveoli and alveolar sacs. An alveolus (al-VE EĒ-ō-lus) is a cup- (dust cells), phagocytes that remove fine dust particles and other shaped outpouching lined by simple squamous epithelium and debris from the alveolar spaces. Also present are fibroblasts that supported by a thin elastic basement membrane; an alveolar sac produce reticular and elastic fibers. Underlying the layer of type consists of two or more alveoli that share a common opening I alveolar cells is an elastic basement membrane. On the outer (Figure 23.10a, b). The walls of alveoli consist of two types surface of the alveoli, the lobule’s arteriole and venule disperse of alveolar epithelial cells (Figure 23.11). The more numerous into a network of blood capillaries (see Figure 23.10a) that type I alveolar cells are simple squamous epithelial cells that consist of a single layer of endothelial cells and basement form a nearly continuous lining of the alveolar wall. Type II membrane. alveolar cells, also called septal cells, are fewer in number and The exchange of O2 and CO2 between the air spaces in are found between type I alveolar cells. The thin type I alveolar the lungs and the blood takes place by diffusion across the cells are the main sites of gas exchange. Type II alveolar cells, alveolar and capillary walls, which together form the respiratory rounded or cuboidal epithelial cells with free surfaces containing membrane. Extending from the alveolar air space to blood microvilli, secrete alveolar fluid, which keeps the surface plasma, the respiratory membrane consists of four layers between the cells and the air moist. Included in the alveolar fluid (Figure 23.11b): Figure 23.11 Structural components of an alveolus. The respiratory membrane consists of a layer of type I and type II alveolar cells, an epithelial basement membrane, a capillary basement membrane, and the capillary endothelium. The exchange of respiratory gases occurs by diffusion across the respiratory membrane. Monocyte Reticular fiber Elastic fiber Type II alveolar (septal) cell Respiratory membrane Alveolus Diffusion Red blood cell of O2 Type I alveolar cell Diffusion Capillary endothelium Alveolar of CO2 Capillary basement macrophage membrane Epithelial basement Alveolus membrane Red blood cell Type I alveolar in pulmonary cell capillary Interstitial space Alveolar fluid with surfactant (a) Section through an alveolus showing its cellular components (b) Details of respiratory membrane 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 889 Team B venus:JWQY057:ch23: RESPIRATORY SYSTEM ANATOMY 889 1. A layer of type I and type II alveolar cells and associated poxia (low O2 level). In all other body tissues, hypoxia causes alveolar macrophages that constitutes the alveolar wall dilation of blood vessels to increase blood flow. In the lungs, 2. An epithelial basement membrane underlying the alveo- however, vasoconstriction in response to hypoxia diverts pul- lar wall monary blood from poorly ventilated areas of the lungs to well- ventilated regions. This phenomenon is known as ventilation– 3. A capillary basement membrane that is often fused to the perfusion coupling because the perfusion (blood flow) to each epithelial basement membrane area of the lungs matches the extent of ventilation (airflow) to 4. The capillary endothelium alveoli in that area. Despite having several layers, the respiratory membrane is Bronchial arteries, which branch from the aorta, deliver very thin—only 0.5 m thick, about one-sixteenth the diameter oxygenated blood to the lungs. This blood mainly perfuses the of a red blood cell—to allow rapid diffusion of gases. It has been muscular walls of the bronchi and bronchioles. Connections ex- estimated that the lungs contain 300 million alveoli, providing ist between branches of the bronchial arteries and branches of an immense surface area of 70 m2 (750 ft2 )—about the size of a the pulmonary arteries, however; most blood returns to the heart racquetball court—for gas exchange. via pulmonary veins. Some blood, however, drains into bronchial veins, branches of the azygos system, and returns to Blood Supply to the Lungs the heart via the superior vena cava. The lungs receive blood via two sets of arteries: pulmonary  CHECKPOINT arteries and bronchial arteries. Deoxygenated blood passes 8. Where are the lungs located? Distinguish the parietal through the pulmonary trunk, which divides into a left pul- pleura from the visceral pleura. monary artery that enters the left lung and a right pulmonary 9. Define each of the following parts of a lung: base, apex, artery that enters the right lung. (The pulmonary arteries are costal surface, medial surface, hilum, root, cardiac notch, the only arteries in the body that carry deoxygenated blood.) lobe, and lobule. Return of the oxygenated blood to the heart occurs by way of 10. What is a bronchopulmonary segment? the four pulmonary veins, which drain into the left atrium 11. Describe the histology and function of the respiratory (see Figure 21.29 on page 820). A unique feature of pulmonary membrane. blood vessels is their constriction in response to localized hy- Alveolar macrophage Alveolus (dust cell) Type II alveolar (septal) cell Type I alveolar (squamous pulmonary epithelial) cell Alveolus LM 1000x (c) Details of several alveoli ? How thick is the respiratory membrane? 2568T_c23_874-920.qxd 1/26/08 5:09 PM Page 890 Team B venus:JWQY057:ch23: 890 CHAPTER 23 THE RESPIRATORY SYSTEM PULMONARY VENTILATION Figure 23.12 Boyle’s law.  OBJECTIVE The volume of a gas varies inversely with its Describe the events that cause inhalation and exhalation. pressure. The process of gas exchange in the body, called respiration, has Piston three basic steps: Pressure gauge 1. Pulmonary ventilation ( pulmon-  lung), or breathing, is the inhalation (inflow) and exhalation (outflow) of air and in- 1 1 volves the exchange of air between the atmosphere and the alve- 0 2 0 2 oli of the lungs. 2. External (pulmonary) respiration is the exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries across the respiratory membrane. In this process, Volume = 1 liter Volume = 1/2 liter pulmonary capillary blood gains O2 and loses CO2. Pressure = 1 atm Pressure = 2 atm 3. Internal (tissue) respiration is the exchange of gases between blood in systemic capillaries and tissue cells. In this ? If the volume is decreased from 1 liter to 1/4 liter, how would step the blood loses O2 and gains CO2. Within cells, the meta- the pressure change? bolic reactions that consume O2 and give off CO2 during the production of ATP are termed cellular respiration (discussed in Chapter 25). volume, so that the same number of gas molecules strike less wall area. The gauge shows that the pressure doubles as the gas In pulmonary ventilation, air flows between the atmosphere is compressed to half its original volume. In other words, the and the alveoli of the lungs because of alternating pressure same number of molecules in half the volume produces differences created by contraction and relaxation of respiratory twice the pressure. Conversely, if the piston is raised to increase muscles. The rate of airflow and the amount of effort needed for the volume, the pressure decreases. Thus, the pressure of a gas breathing is also influenced by alveolar surface tension, compli- varies inversely with volume. ance of the lungs, and airway resistance. Differences in pressure caused by changes in lung volume force air into our lungs when we inhale and out when we exhale. For inhalation to occur, the lungs must expand, which increases Pressure Changes During lung volume and thus decreases the pressure in the lungs to Pulmonary Ventilation below atmospheric pressure. The first step in expanding the Air moves into the lungs when the air pressure inside the lungs lungs during normal quiet inhalation involves contraction of the is less than the air pressure in the atmosphere. Air moves out of main muscles of inhalation, the diaphragm and external inter- the lungs when the air pressure inside the lungs is greater than costals (Figure 23.13). the air pressure in the atmosphere. The most important muscle of inhalation is the diaphragm, the dome-shaped skeletal muscle that forms the floor of the Inhalation thoracic cavity. It is innervated by fibers of the phrenic nerves, Breathing in is called inhalation (inspiration). Just before each which emerge from the spinal cord at cervical levels 3, 4, and 5. inhalation, the air pressure inside the lungs is equal to the air Contraction of the diaphragm causes it to flatten, lowering its pressure of the atmosphere, which at sea level is about 760 mil- dome. This increases the vertical diameter of the thoracic cavity. limeters of mercury (mmHg), or 1 atmosphere (atm). For air to During normal quiet inhalation, the diaphragm descends about flow into the lungs, the pressure inside the alveoli must become 1 cm (0.4 in.), producing a pressure difference of 1–3 mmHg lower than the atmospheric pressure. This condition is achieved and the inhalation of about 500 mL of air. In strenuous breath- by increasing the size of the lungs. ing, the diaphragm may descend 10 cm (4 in.), which produces The pressure of a gas in a closed container is inversely pro- a pressure difference of 100 mmHg and the inhalation of portional to the volume of the container. This means that if the 2–3 liters of air. Contraction of the diaphragm is responsible for size of a closed container is increased, the pressure of the gas about 75% of the air that enters the lungs during quiet breathing. inside the container decreases, and that if the size of the Advanced pregnancy, excessive obesity, or confining abdominal container is decreased, then the pressure inside it increases. This clothing can prevent complete descent of the diaphragm. inverse relationship between volume and pressure, called The next most important muscles of inhalation are the exter- Boyle’s law, may be demonstrated as follows (Figure 23.12): nal intercostals. When these muscles contract, they elevate the Suppose we place a gas in a cylinder that has a movable piston ribs. As a result, there is an increase in the anteroposterior and and a pressure gauge, and that the initial pressure created by the lateral diameters of the chest cavity. Contraction of the external gas molecules striking the wall o