Handbook of Anatomy and Physiology of the Upper Aerodigestive Tract PDF

5.0 Anatomy and Physiology of the Upper Aerodigestive Tract The upper aerodigestive tract is composed of the nasal cavity, nasopharynx, oral cavity, oropharynx, hypopharynx, larynx, trachea, and esophagus. The complex anatomy and physiology supports basic functions in respiration, phonation, de...

5.0 Anatomy and Physiology of the Upper Aerodigestive Tract The upper aerodigestive tract is composed of the nasal cavity, nasopharynx, oral cavity, oropharynx, hypopharynx, larynx, trachea, and esophagus. The complex anatomy and physiology supports basic functions in respiration, phonation, deglutition, and the special sense apparatus for the olfactory and gustatory systems. Important aspects of anatomy and physiology are reviewed here. Nasal and paranasal sinus anatomy and physiology are covered in Chapter 4.0. ◆ Oral Cavity General The vestibule includes the mucosal surface of the lips, buccal mucosa, and buccal/lateral surfaces of the alveolar ridges. The remainder of the oral cavity includes the more medial structures, including the hard and soft palate, mobile tongue (anterior two-thirds), and the oral floor. The oral floor contains the sublingual salivary glands, and the openings of the submandibular ducts (Wharton’s ducts), draining the submandibular glands, are found throughout on either side of the midline. The frenulum attaches the anterior tongue to the midline oral floor. Minor salivary glands coat the oral cavity and pharynx. Musculature The vestibule includes the orbicularis oris, various levators and depressors, as well as the buccinator, all muscles of facial expression. Tongue muscu- lature involves both intrinsic muscles and extrinsic muscles, including the genioglossus, hyoglossus, and styloglossus, all of which are innervated by the hypoglossal nerve. Blood Supply The lingual artery is the primary blood supply to the tongue. The facial artery, a branch of the external carotid, supplies the vestibule via the superior and inferior labial arteries. The greater and lesser palatine foramina in the lateral hard palate house the greater and lesser palatine arteries, branches of the maxillary artery. Lymphatic Drainage Facial lymphatics drain primarily to submental, submandibular, and facial nodes of level 1, while the anterior tongue lymphatics drain to upper jugular nodes of level 2, often bilaterally. Nerve Supply The hypoglossal nerve, cranial nerve (CN) XII, is the motor supply to the tongue. The lingual nerve (a branch of the mandibular nerve, CN V3) provides 271 272 Laryngology and the Upper Aerodigestive Tract sensation, and taste fibers of the chorda tympani, to the anterior two-thirds of the tongue; CNs IX and X innervate taste buds of the posterior tongue and the base of the epiglottis, respectively. The facial nerve (CN VII) is the motor supply to the orbicularis oris. General sensation to the buccal mucosa is via the second division of the trigeminal nerve (maxillary nerve, CN V2). Physiology On average, 1,500 mL of saliva is produced daily from the parotid, sublingual, submandibular, and minor salivary glands. Detailed swallowing physiology is beyond the scope of this handbook. Briefly, swallowing is divided into active and passive phases. The active phases include a preparatory phase that involves salivation and mastication, and a second oral phase that involves bolus propulsion posteriorly. In the passive phase, CNs IX and X control involuntary laryngeal protective mech- anisms and peristalsis. ◆ Pharynx General The pharynx extends from the skull base to the sixth cervical vertebra (C6) and is divided into the nasopharynx, superior to the palate; the oropharynx, extending from the palate to the hyoid and from the circumvallate papillae anteriorly; and the hypopharynx, inferior to the hyoid, including the piri- form recesses, posterior wall, and postcricoid region (Fig. 5.1). The cervical esophagus extends inferiorly, and the laryngotracheal complex sits anteromedially. Waldeyer’s ring of lymphoid tissue includes the adenoids (pharyngeal tonsil) of the nasopharynx, the palatine tonsils of the oropharynx, and the lingual tonsil lining the base of the tongue. Taste buds and minor salivary glands exist in this region as well. The auditory tubes (eustachian tubes) open in the lateral nasopharynx. Musculature The superior, middle, and inferior pharyngeal constrictors surround the pharynx, enveloped by the visceral layer of cervical fascia. The palatopharyngeus and stylopharyngeus are supportive. The palatoglossus and palatopharyngeus form the tonsillar pillars. Blood Supply The lingual artery supplies the tongue. The palatine tonsils are supplied by external carotid branches via the facial artery, lingual artery, lesser palatine artery, descending palatine artery, and ascending pharyngeal artery. Lymphatic Drainage Rich bilateral drainage supplies the base of the tongue and piriform recesses and drains to levels 2 through 4. The tonsils drain primarily to the jugulodigastric region.  Anatomy and Physiology of the Upper Aerodigestive Tract 273 Basilar part of occipital bone Choana Torus tubarius Nasopharynx Eustachian tube Pharyngeal recess Salpingopharyngeal fold Oropharynx Soft palate Uvula Palatine tonsil Root of tongue Laryngopharynx Epiglottis Aryepiglottic fold Cuneiform tubercle Corniculate tubercle Esophagus Piriform recess Trachea Fig. 5.1 Opened posterior view of the pharynx, demonstrating the boundaries of the nasopharynx, oropharynx, and hypopharynx. (Used with permission from Van de Water TR, Staecker H. Otolaryngology: Basic Science and Clinical Review. New York: Thieme; 2006:553.) Nerve Supply The palatine tonsils have sensory supply from the glossopharyngeal nerve (CN IX) and the lesser palatine nerve (branch of the maxillary nerve, CN V2). Referred otalgia is common. CNs IX and X supply motor and sensory innervation to the hypopharynx. Physiology Swallowing is discussed with the physiology of the oral cavity, above. ◆ Larynx General The larynx can be considered to be a complex valve that regulates airflow. It is a dynamic organ that is involved with both the respiratory/vocal system and the digestive tract because of its position in the pharynx. Its lumen continues superiorly with the pharynx and inferiorly with the trachea; posteroinferiorly it is separated from the pharyngoesophageal lumen. The larynx is divided into the supraglottis, which includes the epiglottis, ary- tenoids, aryepiglottic fold, false vocal fold, and ventricle; the glottis, which is 1 cm inferior to the laryngeal inlet and includes the true vocal folds; and the subglottis, which extends inferiorly to the inferior border of the cricoid cartilage ring (Fig. 5.2). 274 Laryngology and the Upper Aerodigestive Tract 1 Supra- glottis 2 5 Transglottic 4 Glottis space 3 Sub- 6 glottis 7 8 Fig. 5.2 Compartments and individual structures in the larynx. 1. The aryepiglottic fold, forming the boundary between the larynx and hypopharynx. 2. The piriform recess, which belongs to the hypopharynx. 3. Vocal ligament. 4. Anterior commissure. 5. Thyroid cartilage. 6. Cricoid cartilage. 7. Thyroid gland. 8. Trachea. (Used with permission from Behrbohm H et al. Ear, Nose, and Throat Diseases: With Head and Neck Surgery, 3rd ed. New York: Thieme; 2009:293.) Skeleton Three unpaired cartilages form the main laryngeal structure (Fig. 5.3). These are the epiglottis, the thyroid cartilage (from the Greek thyreos, meaning oblong shield), and the cricoid (from the Greek krikos, meaning ring). Three paired cartilages constitute the remainder of the laryngeal skeleton: the ary- tenoids, the corniculates, and the cuneiforms. Anterosuperiorly, the larynx is connected to the hyoid bone by the thyrohyoid membrane and muscle, and inferiorly it joins the trachea. Posteriorly, the larynx meets the muscular wall of the pharynx, with the cervical vertebrae posterior to this layer. The thyroid and cricoid cartilages are hyaline cartilage, which may ossify with age. The inferior horns of the thyroid cartilage articulate with the cricoid cartilage; the paired arytenoids articulate with the cranial border of the cricoid lamina. Both of these articulations are synovial joints. Soft Tissue Externally, the important membranes include the thyrohyoid membrane, the cricothyroid membrane, and the cricotracheal ligament. Internally, the membranous lining of the larynx is the quadrangular membrane superiorly, extending to the vestibular fold or false vocal fold, and the cricovocal mem- brane or conus elasticus, extending from the true vocal fold inferiorly. Paired aryepiglottic folds define the opening into the laryngeal lumen superiorly. Lateral and inferior are the piriform recesses, which funnel food and liquid into the esophagus. The paired vocal folds extend from the vocal process of the arytenoids dorsally to the thyroid cartilage ventrally at the anterior commissure. The structure of the vocal folds includes the vocal ligament, lateral cricothyroid ligament, median cricothyroid ligament, the vocalis muscle (thyroarytenoid), and the mucosal covering.  Anatomy and Physiology of the Upper Aerodigestive Tract 275 a b c Body of hyoid bone Lesser horn Epiglottis Sterno- Medial Greater horn Thyroepiglot- cleidomas- thyrohyoid tic ligament toid muscle Foramina for ligament superior Lateral Thyroid Hyoid laryngeal thyrohyoid gland bone artery and ligament superior Thyroid Corniculate Clavicle laryngeal nerve cartilage cartilage Sternum Superior horn Medial Arytenoid cricothyroid Thyrohyoid cartilage ligament membrane Cricoid Inferior horn cartilage Cricoid cartilage Cricothyroid lamina Arch of joint Tracheal cricoid Cricotracheal cartilages cartilage ligament Membranous Tracheal Annular posterior cartilages ligaments of trachea wall Fig. 5.3 Anatomy of the laryngeal bones and cartilage. (Used with permission from Probst R, Grevers G, Iro H. Basic Otorhinolaryngology: A Step-by-Step Learning Guide. New York: Thieme; 2006:338.) Musculature The posterior cricoarytenoid exclusively opens (abducts) the vocal folds. The lateral cricoarytenoid and transverse arytenoid (interarytenoid) closes the vocal folds, along with the thyroarytenoid. The thyroarytenoid and the cricothyroid place the vocal folds under tension. Blood Supply Arterial supply to the supraglottis arises from the external carotid via the superior laryngeal artery. The inferior laryngeal artery, arising from the sub- clavian artery via the thyrocervical trunk, supplies the subglottis. Venous drainage is to the internal jugular and brachiocephalic veins. Lymphatic Drainage The supraglottis has rich bilateral lymphatic drainage, with connections via the preepiglottic space. The glottis has few lymphatics. The subglottis also has rich bilateral drainage via paratracheal and pretracheal channels. The lymphatic drainage influences the frequency of metastatic spread of laryn- geal carcinomas based on the sites of involvement of the primary tumor. Nerve Supply The vagus nerve (CN X) supplies the larynx. The superior laryngeal nerve has an external branch, providing motor function to the cricothyroid muscle, and an internal branch, providing sensation to the supraglottis and glottis. The recurrent laryngeal nerve provides motor supply to all other internal laryngeal muscles. On the left, the recurrent nerve passes around the aortic arch; on the right, it passes around the subclavian artery. Both recurrent nerves then ascend along the tracheoesophageal groove to enter the larynx at the inferior cornu of the thyroid cartilage. Importantly, the recurrent laryngeal nerve may branch in the neck prior to entering the larynx. (A 276 Laryngology and the Upper Aerodigestive Tract nonrecurrent right laryngeal nerve may occur if an aberrant subclavian artery is present.) Physiology Briefly, the basic functions of the larynx include airway protection, speech, and respiration. The larynx acts as a sphincter, in concert with pharyngeal structures, to prevent airway aspiration. This is facilitated via epiglottic tilt and contraction of the aryepiglottic folds, false vocal folds, true vocal folds, and adductors. Detailed discussion of the physiology of phonation is beyond the scope of this book. ◆ Esophagus General The esophagus lies posterior to the trachea. The esophageal opening is ~15 cm from the upper incisors at the lower border of the cricoid (C6), and the gastroesophageal junction is ~40 cm in adults. The upper esophageal sphinc- ter is formed by the cricopharyngeus muscle at the esophageal opening. A middle physiologic sphincter exists at ~25 cm due to the aortic arch and left bronchus. The lower esophageal sphincter is at the gastroesophageal junction. The esophageal wall has a mucosa, submucosa, muscle layer, and outer fibrous adventitia. There are external longitudinal muscle fibers and internal circular fibers. The superior third is striated muscle, the middle third is mixed, and the inferior third is smooth muscle. The mucosa is strat- ified squamous, with a transition to columnar epithelium at the junction with the stomach. Blood Supply Superiorly, supply is via branches from the inferior thyroid artery originating from the thyrocervical trunk. In the thorax, supply is segmental via branches of the thoracic aorta or via intercostal vessels. Inferiorly, there are branches from the left gastric artery. There is a venous plexus, and drainage parallels supply generally. Lymphatic Drainage The cervical lymphatic system includes the deep cervical and paratracheal nodes; the thoracic lymphatics are composed of the posterior mediastinal and tracheobronchial nodes. The abdominal lymphatic system incorporates the left gastric and celiac nodes. Nerve Supply The esophagus is served by the glossopharyngeal and vagus nerves and the sympathetics. The myenteric plexus of Auerbach lies between the longitudinal and circular muscle layers. Physiology The esophageal phase of swallowing occurs as the bolus passes the upper esophageal sphincter. Primary peristalsis has an initial rapid inhibitory