Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University

1. The Pharyngeal Apparatus Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University

2. INTRODUCTION • Branchial is derived from the Greek word branchia, gill (fish) and in human is called pharyngeal and not branchial • Pharyngeal apparatus is used in human embryo instead of branchial apparatus when describing the development of the head and neck regions of the human embryos • Pharyngeal apparatus consists of pharyngeal arches, pouches, grooves, and membranes • These embryonic structures contribute to the formation of the lateral and ventral regions of the head and neck

3. Pharyngeal Arches • They develop early in the 4th week as a neural crest cells migrate into the future head & neck regions • By the end of the 4th week, FOUR pairs of pharyngeal arches are visible [1,2,3,4]. The 5th & 6th are rudimentary and are not visible • The first (mandibular arch) & second (hyoid arch) • The arches are separated by grooves externally and pouches internally and numbered in craniocaudal sequence • Stomodeum (primordial mouth) which is separated from the cavity of the primordial pharynx by a bilaminar membrane (oropharyngeal membrane) which ruptures by 26 days, bringing the pharynx and foregut into communication with the amniotic cavity

4. Pharyngeal Arch Components • Pharyngeal arch artery that arises from the truncus arteriousus of the primordial heart and passes around the primordial pharynx to enter the dorsal aorta • A cartilaginous rod that forms the skeleton of the arch • A muscular component that differentiates into muscles in the head & neck • Nerves that supply the mucosa and muscles derived from the arch (derived from the neuroectoderm of the primordial brain)

5. Fate of the Pharyngeal Arches • The pharyngeal arches contribute extensively to the formation of the face, nasal cavities, mouth, larynx, pharynx, and neck • During the 5th week, the 2nd arch enlarges and overgrows the 3rd & 4th arches, forming and ectodermal depression-the cervical sinus • By the end of the 7th week, the 2nd-4th pharyngeal grooves and the cervical sinus have disappeared, giving the neck a smooth contour

6. Derivatives of the Pharyngeal Arch cartilages • The dorsal end of the 1st pharyngeal arch cartilage form (malleus & incus) bones of the middle ear and its middle part regress and gives anterior ligament of malleus and sphenomandibular ligament. Ventral part gives the mandible • 2nd arch cartilage form [stapes of middle ear and styloid process of the temporal bone] and stylohyoid ligament. The lesser cornu and the superior part of the body of hyoid bone are formed by the ventral part of the arch • 3rd arch cartilage form the greater cornu and the inferior part of the body of the hyoid bone • 4th-6th arch cartlages form the laryngeal cartilages except for the epiglottis which develops from the mesenchyme in the hypopharyngeal eminence. The 5th arch is rudimentary and has no derivatives

7. Derivates of the Pharyngeal Arch Muscles

8. Derivates pf Pharyngeal Arch Nerves

9. Pharyngeal Pouches • The primordial pharynx widens cranially where it joins the stomodeum and narrows caudally where it joins the foregut –esophagus • The endoderm of the pharynx lines the internal aspects of the pharyngeal arches and passes into diverticula (pharyngeal pouches) • The pouches develop into carniocaudal sequence between the arches • They are FOUR well defined pairs of pharyngeal pouches and the 5th pair is absent • The endoderm of the pouches contacts the ectoderm of the grooves and together they form the double layered pharyngeal membranes that separate the pouches from the grooves

10. Derivatives of the Pharyngeal Pouches- The 1st Pharyngeal Pouch • It gives rise to • The tympanic cavity • Mastoid antrum • Pharyngotympanic tube (auditory tube)

11. Derivatives of the Pharyngeal Pouches- The 2nd Pharyngeal Pouch • At approximately 20 weeks, this pouch is associated with the development of the palatine tonsil form the mesenchyme contents of this pouch

12. Derivatives of the Pharyngeal Pouches- The 3rd Pharyngeal Pouch • The following structures are derived from the 3rd pouch • Thymus • Parathyroid glands (inferior parathyroid glands)

13. Derivatives of the Pharyngeal Pouches- The 4th Pharyngeal Pouch • Superior parathyroid glands derived from the 4th pharyngeal pouch

14. Pharyngeal Grooves • They disappear except for the 1st pair, which persists as the external acoustic meatus

15. Pharyngeal Membranes • They disappear except for the 1st pair, which becomes the tympanic membranes

16. Pharyngeal (Branchial) Anomalies • Branchial (cervical) sinuses: it result from failure of the 2nd pharyngeal groove and cervical sinus to obliterate (anterior or lateral side of the neck) • External • Internal • Branchial fistula • Piriform sinus fistula ( remnants of the ultimopharyngeal body) the fistula traces the path of this embryonic body to the thyroid gland • Branchial cysts • Branchial vestiges • First arch syndrome • (Treacher Collins syndrome (mandibulofacial dysostosis) • Pierre Robin syndrome (hypoplasia of the mandible, cleft palate, and eye and ear defects present)

17. Congenital anomalies of Thymus & Parathyroid Glands • DiGeorge Syndrome (No thymus and parathyroid glands and cardiac outflow problems) • Accessory thymic tissue • Ectopic parathyroid glands • Abnormal number of parathyroid glands

18. Development of the Thyroid Gland • The first endocrine gland to develop in the embryo by 24 day after fertilization • It develops from a downgrowth from the floor of the primordial pharynx in the region where the tongue develops (endodermal thickening-thyroid primordium/pouch) • It descend in the neck, passing ventral to the developing hyoid bone & laryngeal cartliages • Cit is connected for a short time to the tongue by a thyroglossal duct • It divides to two lobes conneted by isthmus which lie oppsoing the 2nd & 3rd tracheal rings • By 7 weeks, the thyroid has assumed it definitive shape. Thyroglossal has normally disappeared and it proximal end persist as a small pit in the dorsum of the tongu (foramen cecum) • The parafolllicular cells (C cells) are derived from the ultimopharyngeal bodies, which are derived from the 4th pharyngeal pouch pair • A pyramidal lobe differentiate from the distal end of the thyroglossal duct and attches to the hyoid bone by fibrous tissue and/or smooth muscle (levator muscle of the thyroid gland)

19. Thyroid Gland Congenital Anomalies • Congenital hypothyroidism • Thyroglossal duct cysts & sinuses • Ectopic thyroid gland • Accessory thyroid tissue • Agenesis of the thyroid gland

20. Development of The Tongue • At the end of the 4th week, median lingual swelling (tongue bud) in the floor of the primordial pharynx just rostral to the foramen cecum. This swellings do not form a recognizable part of the adult tongue • Two lateral lingual swelling develop on each side of the median tongue bud. These form the anterior two thirds (oral part) of the tongue. The fusion site is indicated by the midline groove of the tongue and internally by the fibrous lingual septum • The three lingual swellings result from the proliferation of mesenchyme in the ventromedial parts of the 1st pair of pharyngeal arches • The formation of the posterior third of the tongue (pharyngeal part) is indicated in the fetus by two elevations that develop caudal to the foramen cecum • The copula forms by the fusion of the ventromedial parts of the 2nd pharngeal arches pair • The hypopharyngeal eminence develops caudal to copula from the mesenchyme in the ventromedial parts of the third and fourth pairs of arches • The line of fusion of the anterior 2/3 and posterior 1/3 of the tongue is indicated by a V-shaped groove (terminal sulcus)

21. Development of The Tongue- Lingual papillae & Taste Buds Lingual papillae appear toward the end of the 8th week. The vallate and foliate papillae appear first. The fungioform papillae appear later. The filiform papillae develop during the early fetal period (10-11 weeks) Taste buds develop during weeks 11-13 by inductive interaction between epithlial cells of the tongue and invading gustatory nerve cells from the chorda tympani, glossopharyngeal, and vagus nerve Fetal facial responses can be induced by bitter-tasting substances at 26-28 weeks, indicating that reflex pathways between taste buds and facial muscles are established by this stage

22. Development of The Tongue- Nerve Supply of the Tongue • The development of the tongue explains its nerve supply • The sensory supply to anterior 2/3 is from the lingual branch of the mandibular division of the (CN-V, trigeminal nerve), nerve of the 1st pharngeal arch which form the median and lateal lingual swellings • The chorda tympani branch of the (CN-VII, facial nerve) supplies the taste buds in the anterior 2/3, except for the vallate papillae which are supplied by the (CN-IX, glossopharyngeal nerve) of the third pharyngeal arch. This is because the 2nd arch component (copula) is overgrown by the third arch • Posterior third of the tongue is innervated by (CN-IX, glossopharyngeal nerve) of the third pharyngeal arch • The superior laryngeal branch of the (CN-X, vagus nerve) supplies small area of the tongue anterior to epiglottis • All muscles of the tongue is innervated by (CN-XII, Hypoglossal nerve) except for the palatoglossus muscle, which is supplied from the pharyngeal plexus by fibers arising from the (CN-X, vagus nerve)

23. Congenital Anomalies of the Tongue Congenital lingual cycsts & fistula Ankyloglossia Macroglossia Microglossia Bifid or cleft tongue (Glossoschisis)

24. Development of the Salivary Glands • During 6th & 7th weeks of the embryonic period, the salivary glands begin as solid epithelial buds from the primordial oral cavity. The club-shaped ends of these epithelial buds grow into the underlying mesenchyme • The connective tissue in the glands is derived from the neural crest cells • All parenchymal (secretory) tissue arises by proliferation of the oral epithelium • Parotid glands first to appear and then submandibular glands and eventually the sublingual (8th week)

25. Development of the Face • The five facial primordia that appears as prominences around the stomodeum are: • The single frontonasal prominence • The paired maxillary prominences • The paired mandibular prominences

26. Development of the Face • The frontal nasal prominence forms the forehaed and dorsum and apex of the nose • The lateral nasal prominences form the alae of the nose • The medial nasal prominences form the nasal septum, ethmoid, and cribriform plate • Maxillary prominences form the upper cheek regions and the upper lip • The mandibular prominences give rise to the chin, lower lip, and lower cheek regions

27. Development of the Nasal Cavities • As the face develops, the nasal placodes become depressed, forming nasal pits • Proliferation of the surrounding mesenchyme forms the medial & lateral nasal prominences, which results in deepening of the nasal pits and formation of primordial nasal sacs • Each nasal sac grows dorsally, and ventral to the developing forebrain

28. Development of the Nasal Cavities • The nasal sacs are separated from oral cavity by the oronasal membrane • This membrane ruptures by the end of the 6th week bringing both cavities into communication. Temporary epithelial plugs are formed in the nasal cavities from cell proliferation and this plug disappear between 13-15 weeks • The regions of continuity between nasal, and oral cavities are the primordial choanae, which lie posterior to the primary palate. After the secondary palate develops, the choanae are loacted at the junction of the nasal cavity and pharynx • Superior, middle, and inferior nasal conchae develops as elevations of the lateral walls of the nasal cavities • Ectodermal epithelium in the roof of each nasal cavity becomes specialized to form olfactory epithelium, olfactory nerve, and bulb

29. Paranasal Sinuses Maxillary sinuses develops during late fetal life The remainder (ethmoid, frontal , & sphenoid air sinuses) develop after birth They develop from outgrowths or divericula of the walls of the nasal cavities and become pneumatic extensions of the nasal cavities in the adjacent bones

30. Development of the Palate • The palate develops in two stages: • The development of a primary palate • The development of a secondary palate • Palatogenesis begins in the 6th week but the development of the palate is not completed until the 12th week

31. Development of the Palate- Primary Palate • Early in the 6th week, the primary palate-median palatal process (intermaxillary segment) begins to develop • Initially, this segment, formed by merging of the medial nasal prominences, is a wedge-shaped mass of mesenchyme between the internal surfaces of the maxillary prominences of the developing maxillae • The primary palate forms the anterior/midline aspect of the maxilla, the premaxillary part of the maxilla • It represents only a small part of the adult hard palate anterior to the incisive fossa

32. Development of the Palate-Secondary Palate • It is the primordium of both the hard and soft parts of the palate • It starts to develop by 6th week from two mesenchymal projections that extend from the internal aspects of the maxillary prominences (lateral palatal processes (horizontal position above the tongue)-hard palate formed when ossification occurs • The posterior part of the maxillae and palatal processes do not become ossified.. They extend posteriorly beyond the nasal septum and fuse to form the soft palate including its soft conical projection (uvula) • The nasal septum develops as a downgrowth from internal parts of the merged medial nasal prominences

33. Developmental Anomalies of the Face & Palate • Cleft lip & cleft palate • anterior, posterior, unilateral, bilateral, median cleft lip • Cleft palate with or without a cleft lip or partial or complete • Facial Clefts • Congenital microstomia • A single nostril • Bifid nose

34. Developmental Anomalies of the Face & Palate

35. The Pharyngeal Arches Video