anatomy and embryology of the pharynx1

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