Anatomy and Embryology of the Pharynx Jared Bradley Turner, MD January 7, 2005

branchial/pharyngeal apparatus: Embryology Components of branchial/pharyngeal apparatus: Pharyngeal arches Pharyngeal pouches Pharyngeal clefts/grooves

Pharyngeal (branchial) arches Derived from neural crest cells Resemble fish gills (branchia) Begin to develop early in the 4th week By end of 4th week, four pairs of arches are visible on the surface (not 5th and 6th ) and a buccopharyngeal membrane ruptures forming communication between primitive oral cavity and foregut

Pharyngeal arches (cont.) Contribute to the formation of the neck as well as the face. Visible structures at 42 weeks: 1st arch: mandibular prominence, maxillary prominences, and the frontonasal prominence

Pharyngeal arches (cont.) Core of mesenchymal tissue covered by surface ectoderm (outside) and by endodermal epithelium (inside) Ectoderm -> skeletal Mesoderm -> muscles with accompanying nerve Arterial component (aortic arches) Therefore, each arch carries nerve, muscle, bone and blood supply

First pharyngeal arch Maxillary process (dorsal) Premaxilla, maxilla, zygomatic bone, portion of temporal bone Mandibular process (ventral) Contains Meckel’s cartilage which disappears except for dorsal end (incus & malleus) and mandible

First pharyngeal arch Muscles of mastication, digastric (ant belly), mylohyoid, tensor tympani and tensor palatini Therefore, the accompanying motor nerve is the mandibular branch of trigeminal (V2) and sensory are V1, V2, and V3 1st aortic arch practically disappears but forms the maxillary artery

Second pharyngeal arch Reichert’s cartilage – stapes, styloid process, stylohyoid ligament, lesser horn and upper part of the hyoid Muscles include: stapedius, stylohyoid, digastric (post belly), auricular, and those of facial expression Facial nerve (CN VII) 2nd aortic arch – stapedial & hyoid arteries

Third pharyngeal arch Cartilaginous contributions include greater horn and lower part of hyoid Sole muscle: stylopharyngeus CN IX (Glossopharyngeal nerve) 3rd aortic arch (quite large): common carotid, 1st portion of internal carotid (remainder dorsal aorta), and external carotid

Fourth & sixth pharyngeal arch Cartilaginous contributions to larynx derived from fusion: thyroid, cricoid, arytenoid, corniculate, and cuneiform Muscles of 4th: cricothyroid, levator palatini, and pharyngeal constrictors are innervated by SLN (CN X) Muscles of 6th: intrinsics of larynx are innervated by RLN (CN X) 4th aortic arch: L->arch of aorta & R->subclavian 6th aortic arch: L & R pulmonary with ductus arteriosus on left

Pharyngeal pouches (5) 1st:tubotympanic recess-> middle ear & eustacian tube -> TM 2nd palatine tonsil/fossa 3rd: inferior parathyroid (dorsal), thymus (ventral) 4th: superior parathyroid 5th: ultimobranchial body -> calcitonin producing C cells (parafollicular)

Pharyngeal clefts/grooves (4) 1st: external auditory meatus 2nd-4th : epicardial ridge and cervical sinus (disappears)

Anatomy of the pharynx

Anatomy (cont.) Extends from base of skull to inferior border of cricoid cartilage anteriorly and inferior border of C6 posteriorly Widest portion (5cm) at hyoid Narrowest portion (1.5cm) at caudal end Divided into 3 parts: nasopharynx, oropharynx, and laryngo(hypo)pharynx

Nasopharynx Respiratory function Anterior: choana (posterior nasal aperture) Posterior: pharyngobasilar membrane and superior constrictor muscle Superior: basilar portion of occipital bone Inferior: soft palate

Oropharynx Digestive function Anterior: anterior tonsillar pillar Posterior: superior constrictor Superior: soft palate Inferior: base of tongue, superior epiglottis Laterally: palatoglossal and palatopharyngeal arches

Hypopharynx Lies posterior to the larynx Superior: superior border of epiglottis and pharyngoepiglottic folds Inferior: inferior border of the cricoid Posterior/lateral: middle & inferior constrictors, bodies of C4-C6 Anterior: laryngeal inlet

Pharyngeal muscles

Pharyngeal muscles External circular and internal longitudinal (opposite in remainder of GI tract) External: 3 constrictors (CN XI via X and ELN/RLN for middle and inferior) function to constrict wall of pharynx during swallow Internal: palatopharyngeus and salpingopharyngeus (CN XI via X) and stylopharyngeus (CN IX) act to elevate pharynx and larynx during speech/swallow

Pharyngeal muscles Tensor veli palatini (V3) tenses soft palate & opens ET during yawn/swallow Levator veli palatini (CN XI via X) elevates palate during swallow/yawn Palatoglossus (CN XI via X) approximates tongue and soft palate

Pharyngeal muscles

Pharyngeal lymphatic drainage Oral cavity I, II, III Oro/hypopharynx deep II, III, IV Nasopharynx II, V, III

Pharyngeal vessels Ascending pharyngeal, Ascending palatine, Tonsillar, Greater/lesser palatine, Inferior/superior thyroid/lingual

Afferent innervation of pharynx