Anatomy and Embryology of the PharynxJared Bradley Turner, MD
January 7, 2005
Embryology
Components of
branchial/pharyngeal apparatus:
1) Pharyngeal arches
2) Pharyngeal pouches
3) 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
Afferent innervation of pharynx