Embryology of Pharyngeal Arches Flashcards
• Pharyngeal/branchial arch
o Each has same basic structure
o Artery, nerve and cartilage
o Originally ectomesenchyme
o Formed from 1st 7 pairs of somitomeres
o Form everything in the head and neck
o Give rise to striated muscles of face, jaws and throat
o Send neural crest cells into the arches during 4th week
o Major source of cartilage, bone, ligament in facial and oral regions
o Ganglia of CN 5, 7, 9, and 10 partly derived from neural crest cells
• Pharyngeal/branchial cleft/groove
o No mesoderm, only endo and ectoderm
1st groove only one that forms adult derivative: external acoustic meatus
• Pharyngeal branchial membrane
o Formed by union of cleft and pouch
1st groove only one that forms adult derivative: tympanic membrane
• Pharyngeal/branchial pouch
o Internal of the cleft
1st, 2nd, 3rd, and 4th & 6th form adult derivatives
-pharyngotympanic tube
-tonsillar sinus/fossa crypts
-inferior parathyroid & thymus
- superior parathyroid & parafollicular cells
• Mandibular arch
o 1st arch (M arch) o Meckel’s cartilage o CN 5 (V2 & V3)- maxillary and mandibular division of trigeminal o Muscles of mastication Anterior belly of digastric Mylohyoid o Maxillary artery-arch 1
Meckel’s cartilage
- 1st arch
- Maxilla & zygomatic bone, mandible (template) & squamous part of temporal
- Malleus, incus, ½ of hyoid
- Sphenomandibular ligament
- Anterior ligament of Malleus
Muscles of mastication:
- tensor tympani,
- tensor veli palatine,
- masseter,
- lateral medial pterygoids
- Anterior belly of digastric
- Mylohyoid
1st Arch Pouch:
Pharyngo-tympanic tube (eustacian or auditory tube)
• Opens up unto pharynx
o Ist arch Groove:
External Acoustic Meatus
1st Arch Membrane
typmanic membrane
• Hyoid arch
o 2nd arch (S arch) o Overgrows clefts of 2nd, 3rd, and 4th arches to form cervical sinus o Reichert’s cartilage o CN 7- facial nerve o Stapedial artery-arch 2
o Reichert’s cartilage
- cartilage of 2nd arch Stapes, styloid process upper body of Hyoid bone lesser cornu bone Stylohoid ligament
o Muscles of 2nd arch
Facial expression muscles
Posterior belly of digastric
Stylohyoid
Stapedius muscle
o Pouch:of 2nd arch
Tonsillar sinus/fossa
• This is where palatine tonsil sits
Surface epithelium of Tonsillar Crypts from endoderm
• 3rd Arch
o CN IX- Glossopharyngeal o Muscles Stylopharngeus o ligaments Lower hyoid Greater cornu (horn) o Pouch: Inferior parathyroid glands from Dorsal Thymus • Ventral: bilateral elongate and hollow primordial come together and thymus descends
Muscles and ligaments of 3rd arch
Muscles Stylopharngeus o ligaments Lower hyoid Greater cornu (horn)
Pouch of 3rd arch
Inferior parathyroid glands from Dorsal
Thymus
• Ventral: bilateral elongate and hollow primordial come together and thymus descends
• 4th & 6th Arches: Larynx Pharynx
o Muscles of larynx and pharynx o Cartilage Laryngeal cartilages • Thyroid • Cricoid • Corniculate • Cuneiform o CN X – Vagus Superior Laryngeal to 4th arch Recurrent laryngeal to 6th arch o Pouch: Dorsal: Superior parathyroid glands Ventral: ultimobranchial body • Parafollicular (C) cells of the thyroid
o Muscles of larynx and pharynx
- 4th and 6th arch derivatives
-Cricothyroid
Levator veli palatine
Constrictors of pharynx
Intrinsic muscles of larynx
laryngeal cartilage
- 4th and 6th arch derivatives o Thyroid • Cricoid • Corniculate • Cuneiform
4th and 6th arch pouch
Dorsal: Superior parathyroid glands
Ventral: ultimobranchial body
• Parafollicular (C) cells of the thyroid
• Aortic Arches
o As pharyngeal arches develop, aortic arches supply them
o 6 aortic arches develop
o 1st Aortic arch – maxillary arteries
o 2nd Aortic Arch –stapedial arteries
o 3rd aortic arch–carotid
Proximal: common carotid
Distal: internal carotid with dorsal aorta
• Branchial abnormalities:
o Usually results from persistence of 2nd groove and pouche o Opens into side of neck o 10% of cases ar bilateral o Cyst- o Sinus o Fistula-
branchial cyst
- mucosal lined, fluid filled cavity
- Usually at angle of mandible where 2nd and 3rd come together or at the anterior border of the SCM muscle
- Accumulate fluid and cellular debris
branchial sinus
- blind-ending pit with one opening
branchial fistula
2 openings
Often drain cervical cysts
Open along the anterior border of SCM muscle
ascends to pass between internal and external carotid arteries and opens into tonsillar fossa
Treatment is excision
• First Arch syndromes
o Insufficient migration of neural crest cells o Deformed auricle o Perauricular appendage o Defect in cheek o Hypoplasia of mandible o macrostomia o Treacher Collins syndrome/mandibulofacial dysostosis o Pierre Robin Syndrome
o Treacher Collins syndrome/mandibulofacial dysostosis
-1st arch syndrome TCOF1 gene on 5tq31-q34 • Autosomal dominant • 60% new mutation • > paternal age • Uses OMENS to differentiate diseases Malar hypoplasia Downslanting palpebral fissures Deformed external ears Defects of lower eyelids
o Pierre Robin Syndrome
-1st arch syndrom Hypoplasia of mandible Celft palate Defects of eye, ear - clenched fists - SOX9, 50% cases (a sequence)
• 3rd and 4th pouch syndromes
o DiGeorge syndrome
o Goldenhar syndrome
o DiGeorge syndrome
-3rd and 4th arch syndrome
- Microdeletion of Chrom 22
Absence of thymus
• Lots of infections
Malformation of mouth (fish mouth)
Nasal clefts
Cardiac abnormalities
hypoparathyroidism
• 1st and 2nd arch syndromes
o Goldenhar syndrome
-3rd and 4th arch syndrome
-Hemifacial microsomia
• Half of the face usually around the eyes, ears, and the mouth (60%)
• Bilateral in the rest with 10-33% of those more severe on one side
• Majority of cases, right more affected than the left
Oculo-auricular dysplasia
Oculoauricular-vertebral spectrum
Incomplete development of the ear, nose, soft palate and mandible and spinal column
• Van Der Woude syndrome
o Autosomal dominant
o Most common clefting syndrome
o Cleft lip/palate with/without distinctive lip pits
o Tooth agenesis
o No other apparent structural abnormalities
o Pits in 88% and 64% they are the only manifestation
o 25% have no symptoms or minimal like missing teeth or lip pits
o Most common syndrome assoc. with cleft lip and palate
o IRF6 gene
- rare (1/30,000)
- (70% )VWS exonic mutation
- problems with wound healing
• Dumbo rats
o 1st arch syndrome?
o MSX and Dlx homeobox genes expressed in the arches
o big ears, small lower mandible
