Head & Neck Development 2018 PDF

PHARYNGEAL (BRANCHIAL) APPARATUS 4 week: fish Branchial, branchia: Greek, gill Primordial branchial apparatus develops in human but no gill forms Branchial arch pharyngeal arch PHARYNGEAL (BRANCHIAL) APPARATUS pharyngeal pharyngeal pharyngeal pharyngeal arches pouches grooves membranes Early 4th wee...

PHARYNGEAL (BRANCHIAL) APPARATUS 4 week: fish Branchial, branchia: Greek, gill Primordial branchial apparatus develops in human but no gill forms Branchial arch pharyngeal arch PHARYNGEAL (BRANCHIAL) APPARATUS pharyngeal pharyngeal pharyngeal pharyngeal arches pouches grooves membranes Early 4th week: Neural crest cells migrate into head & neck 1st pair (jaw primoridum): surface elevations lateral to pharynx soon other arches appear on each side of future H&N regions end of 4th week: 4 pairs of arches 5th & 6th arches: rudimentary, not visible on surface Arches separated by fissures: pharyngeal grooves (clefts) PHARYNGEAL ARCHES Arches support lateral walls of primordial pharynx 1st Pharyngeal (Mandibular) Arch – Maxillary prominence (process) Maxilla (upper jaw) Zygomatic bone temporal bone, squamous part – Mandibular prominence (process) Mandible (lower jaw) 2nd Pharyngeal (Hyoid) Arch Hyoid bone Primordial mouth (stomodeum): slight depression of surface ectoderm separated from pharynx by bilaminar membrane, oropharyngeal membrane (3rd week) ruptures at 26 days Pharyngeal Arch Components Core of mesenchyme – Original mesenchyme derived from mesoderm, 3rd week – 4th week: most of mesenchyme derived from neural crest cells Ectoderm externally Endoderm internally Pharyngeal Arch Components Neural crest cells differentiate into mesenchyme, producing maxillary & mandibular prominences Skeletal musculature & vascular endothelia derived from original mesenchyme FATE OF PHARYNGEAL ARCHES Face Nasal cavities Mouth Larynx Pharynx Neck FATE OF PHARYNGEAL ARCHES 5th week: 2nd arch enlarges & overgrows 3rd & 4th arches, forming an ectodermal depression - cervical sinus End of 7th week: 2nd - 4th grooves & cervical sinus disappear, smooth contour FATE OF PHARYNGEAL ARCHES Typical pharyngeal arch: – Aortic arch – Cartilaginous rod – Muscular component – Nerve Derivatives of the Aortic Arches (Pharyngeal Arch Arteries) Cardiovascular system Fish: supply blood to capillary network of gills Human embryos: supply arches & then enters dorsal aorta Derivatives of the Pharyngeal Arch Cartilages 1st arch (Meckel) cartilage: – Dorsal end malleus & incus – Middle part Regresses Perichondrium: – anterior ligament of malleus – Sphenomandibular ligament – Ventral part Horseshoe-shaped primordium of mandible, guide its early morphogenesis Cartilage disappears as mandible develops around it by intramembranous ossification Derivatives of the Pharyngeal Arch Cartilages 2nd arch (Reichert) cartilage: – Dorsal end Stapes Styloid process of temporal bone – Part between styloid process & hyoid bone Regresses Perichondrium – Stylohyoid ligament – Ventral end Lesser cornu & superior part of body of hyoid bone Derivatives of the Pharyngeal Arch Cartilages 3rd arch cartilage: – in ventral part of arch – Forms greater cornu & inferior part of body of hyoid bone 4th & 6th arch cartilages: – Fuse to form laryngeal cartilages, except epiglottis Epiglottis develops from mesenchyme in hypobranchial eminence, a prominence in embryonic pharynx that is derived from 3rd & 4th pharyngeal arches Derivatives of the Pharyngeal Arch Muscles Various striated muscles in H&N Musculature of 1st arch: muscles of mastication Derivatives of the Pharyngeal Arch Nerves Each arch supplied by its own CN Facial skin: CN V (trigeminal N), – principal sensory N of H&N and motor N for muscles of mastication – Sensory branches innervate face, teeth, mucous membranes of nasal cavities, palate, mouth, tongue Only maxillary & mandibular branches supply derivatives of 1st arch Derivatives of the Pharyngeal Arch Nerves Facial N (CN VII): 2nd arch Glossopharyngeal N (CN IX): 3rd arch Vagus N (CN X): – Superior laryngeal branch: 4th arch – Recurrent laryngeal branch: 6th arch Nerves of 2nd6th arches have little cutaneous distribution; however, they innervate mucous membranes of tongue, pharynx, larynx PHARYNGEAL POUCHES 4 pairs 1st pair between 1st & 2nd arches 5th pair absent or rudimentary Endoderm of pouches contact with ectoderm of grooves: doublelayered pharyngeal membranes Derivatives of the Pharyngeal Pouches 1st pharyngeal pouch – Tubotympanic recess Expanded distal part – contacts 1st groove, where it later contributes to formation of tympanic membrane (eardrum) Cavity – Tympanic cavity – Mastoid antrum Connection with pharynx – Pharyngotympanic tube (auditory tube, eustachian tube) Derivatives of the Pharyngeal Pouches 2nd pharyngeal pouch – palatine tonsils – Pouch endoderm: surface epithelium and lining of tonsillar crypts – 20 weeks: mesenchyme around crypts: lymphatic nodules 3rd pharyngeal pouch – Dorsal part 6th week: inferior parathyroid gland (parathyroid III) – Ventral part thymus, descends into superior mediastinum – Connection with pharynx reduced to a narrow duct that soon degenerates – Primordia of thymus & parathyroid gland lose connection with pharynx and migrate into neck – Later parathyroid glands separate from thymus & lie on dorsal surface of thyroid gland 4th pharyngeal pouch 6th week, superior parathyroid gland (IV) Parathyroid III descend with thymus, carried to more inferior position than parathyroid IV. This explains why parathyroid III are located inferior to parathyroid IV. 5th pharyngeal pouch When develops, becomes part of 4th pharyngeal pouch& helps to form ultimobranchial body Pharyngeal Grooves (Clefts) 4th & 5th weeks: 4 grooves on each side Separate arches externally 1st pair: external acoustic meatus Other grooves lie in a slitlike depression cervical sinus - and are normally obliterated with sinus as neck develops Pharyngeal Membranes 4th week Epithelia of groove and pouch approach each other Endoderm & ectoderm separated by mesenchyme 1st pharyngeal membrane: tympanic membrane Branchial Sinuses External – Discharge of mucous from orifice in neck Internal – Open into pharynx – Very rare – persistence of proximal part of 2nd pouch – Normally pouch disappears as palatine tonsil develops; normal remnant is tonsillar sinus Branchial Fistula Opens internally into tonsillar sinus & externally in side of neck Persistence of parts of 2nd groove & 2nd pouch Branchial Cysts 3rd&4th arches buried in cervical sinus Remnants of parts of cervical sinus &/or 2nd groove may persist & form a cyst May be associated with branchial sinuses & drain through them anywhere along anterior border of SCM muscle painless swelling in neck DEVELOPMENT OF THE FACE Early 4th week around stomodeum 5 facial primordia: – Single frontonasal prominence (FNP) – Paired maxillary prominences – Paired mandibular prominences 1st arch Prominences produced predominantly by proliferation of neural crest cells that migrate from lower mesencephalon & upper rhombecephalon of neural folds into arches during 4th week DEVELOPMENT OF THE FACE Neural crest cells: – Major source of connective tissue components Cartilage Bone Ligaments in facial & oral regions Myoblasts originating from paraxial & prechordal mesoderm contribute to craniofacial voluntary muscles DEVELOPMENT OF THE FACE FNP surrounds ventrolateral part of brain – Optic vesicles: eyes – Frontal portion: forehead – Nasal part: rostral boundary of stomodeum & nose DEVELOPMENT OF THE FACE Paired maxillary prominences – Lateral boundaries of stomodeum Paired mandibular prominences – Caudal boundary of primitive mouth Mainly between 4th & 8th weeks Lower jaw & lower lip: 1st parts to form – Medial ends of mandibular prominences merge in median plane End of 4th week: bilateral oval thickenings of surface ectoderm-nasal placodes- on inferolateral parts of FNP – Primordia of nose & nasal cavities Mesenchyme in margins of placodes proliferate & produce horseshoeshaped elevations: – Medial & lateral nasal prominences As a result, nasal placodes lie in depressions: – Nasal pits (primordia of anterior nares [nostrils] & nasal cavities) End of 5th week – Primordia of auricles of external ears begin to develop – 6 auricular hillocks (small mesenchymal swellings) form around 1st pharyngeal groove (3 on each side) auricular hillocks: auricle 1st pharyngeal groove: external acoustic meatus (canal) – Initially external ear at level of neck End of 6th week: – Each maxillary prominence begin to merge with lateral nasal prominence along the line of nasolacrimal groove – This establishes continuity between side of nose, formed by lateral nasal prominence, and cheek region formed by maxillary prominence 7-10th week Medial nasal prominences merge with each other and with maxillary and lateral nasal prominences Nasolacrimal duct – Rodlike thickening of ectoderm in floor of nasolacrimal groove – Solid epithelial cord separates from ectoderm & sinks into mesenchyme – Cord canalizes to form duct – Cranial end expands: lacrimal sac – Duct drains into inferior meatus by late fetal period – Atresia of nasolacrimal duct Medial nasal prominences merge: intermaxillary segment – Middle part of philtrum of upper lip – Premaxillary part of maxilla and its associated gingiva (gum) – Primary palate Maxillary prominences: – Lateral parts of upper lip – Most of maxilla – Secondary palate Merge laterally with mandibular prominences Primitive lips and cheeks invaded by mesenchyme from 2nd arch, which differentiates into facial muscles (CN VII), nerve of 2nd arch Mesenchyme in 1st arch: muscles of mastication & a few others: CN V, 1st arch DEVELOPMENT OF THE PALATE primary palate secondary palate Palatogenesis: – Begins at end of 5th week – development not completed until end of 12th week – Most critical period: end of 6th week-beginning of 9th week Primary Palate Early in 6th week –Primary palate – median palatine process develop from deep part of intermaxillary segment of maxilla –Initially this segment is a wedge-shaped mass of mesenchyme between internal surfaces of maxillary prominences of developing maxilla –Forms premaxillary part of maxilla –Represents only a small part of adult hart palate (anterior to incisive fossa) Secondary Palate Primordium of hard & soft parts of palate extending posteriorly from incisive fossa Early in 6th week from two mesenchymal projections that extend from internal aspects of maxillary prominences – Lateral palatine processes (palatal shelves) Secondary Palate initially these structures project inferomedially on each side of tongue As jaws develop, tongue becomes relatively smaller & moves inferiorly 7th&8th weeks: lateral palatine processes elongate& ascend to horizontal position superior to tongue Shelves approach each other & fuse in median plane Also fuse with nasal septum & posterior part of primary palate Nasal Septum Develops as downgrowth from internal parts of merged medial nasal prominences Fusion between nasal septum & palatine processes – begins anteriorly during 9th week – Completed posteriorly by 12th week Bone in primary palate, forming premaxillary part of maxilla, lodging incisor teeth Bone extends from maxilla and palatine bones into palatal shelves, forming hard palate Posterior parts of shelves not ossified, extend posteriorly beyond nasal septum & fuse to form soft palate, including uvula Median palatine raphe: line of fusion of lateral palatine processes Nasopalatine canal in median plane of palate between premaxillary part of maxilla & palatine processes of maxilla Represented in adult by incisive fossa, common opening for small R&L incisive canals irregular suture runs from incisive fossa to alveolar processes of maxilla, between lateral incisor and canine teeth on each side visible in anterior region of palates of young persons suture: fusion of embryonic primary and secondary palates CLEFT LIP and PALATE Anterior cleft anomalies – Cleft lip with or without cleft of alveolar part of maxilla – complete anterior cleft anomaly: Extends through lip & alveolar part to incisive fossa, separating anterior & posterior parts of palate – Deficiency of mesenchyme in maxillary prominences & intermaxillary segment Posterior cleft anomalies – Clefts of secondary or posterior palate, extending through soft & hard regions of palate to incisive fossa, separating anterior & posterior parts of palate Defective development of secondary palate Growth distortions of lateral palatine processes, preventing their medial migration & fusion (A) incomplete unilateral cleft of the lip, (B) unilateral cleft of the lip, alveolus, and palate, (C) bilateral cleft of the lip, alveolus, and palate, (D) isolated (median) cleft palate. Embryological basis of cleft palate Failure of mesenchymal masses in lateral palatine processes to meet & fuse with each other, with nasal septum, and/or with posterior margin of median palatine process Median cleft of upper lip – Extremely rare – Mesenchymal deficiency causing partial or complete failure of medial nasal prominences to merge & form intermaxillary segment Median cleft of lower lip – Very rare – Failure of mesenchymal masses in mandibular processes to merge completely & smooth out embryonic cleft between them