9: Development Of The Pharyngeal Apparatus Flashcards
When do PAs start developing?
Early 4th week
What starts the development of pharyngeal arches?
NCCs migrate into future head and neck
What is the 1st pair of pharyngeal arches referred to as?
The primordial jaw
Core of each PA
Mesoderm + mesenchyme
Where is mesenchyme derived from?
Migratory NCCs (NCCs from neural tube forebrain, midbrain, and hindbrain)
What forms all CT in the head, including dermis and smooth muscle?
Mesenchyme
Head mesoderm is derived from what type of mesoderm?
Paraxial mesoderm
What does lateral plate mesoderm form in the head?
Endothelium
What does prechordal plate mesoderm form in the head?
Extraocular musculature
What covered PAs externally and internally?
Ectoderm and endoderm
Two functions of PAs
- Support lateral walls of primitive pharynx
2. Give rise to facial prominences for craniofacial development
Other name for 1st and 2nd PA cartilages
1st cartilage: Meckel’s cartilage
2nd cartilage: Reichert’s cartilage
What forms the body of the hyoid?
Hypopharyngeal eminence, which forms from PA3 and PA4
Specific nerves supplying 4th and 6th PA
4th: recurrent laryngeal branches, superior laryngeal N
6th: recurrent laryngeal branches
Which is internal vs external, grooves and pouches
Grooves: external
Pouches: internal
What does the 1st groove form?
External acoustic meatus
Where are grooves 2-4?
In the cervical sinus
Development of groove 2
Grows inferiorly to cover cervical sinus (birth defects can occur with this)
What causes First Arch Syndrome?
Insufficient migration of NCCs into first arch
What can be malformed in First Arch Syndrome?
Eyes, ears, mandible, palate
Two syndromes involved in First Arch Syndrome
- Treacher-Collins Syndrome
2. Pierre Robin Sequence
Treacher Collins Syndrome (mandibulofacial dystostosis): S/S
Malar hypoplasia, downward slanting palpebral fissures, defects in lower eyelids, deformed external ears (sometimes internal too)
Genetics of Treacher-Collins Syndrome
Mutation in TCOF1 gene (TREACLE protein); is autosomal dominant
What happens with a TCOF1 mutation?
Ribosome biogenesis is truncated -> increased apoptosis of cranial NCCs
Pierre Robin Sequence
Hypoplasia of mandible, cleft palate, defects in ears and eyes
Genetics of Pierre robin sequence
De novo typically
Initiating defect of Pierre Robin Sequence and the cascade of things that occur from there
- Micrognathia
- Posterior displacement of tongue
- Obstruction of full closure of palate
- Bilateral cleft palate
External cervical sinus
Failure of 2nd groove and cervical sinus to obliterate
How is external cervical sinus detected?
Discharge of mucus
Internal cervical sinus
Persistence of 2nd pouch, opens into tonsillar sinus or near palatopharyngeal arch
Cervical cysts
Remnants of cervical sinus and/or 2nd groove -> slowly enlarging painless cyst in neck
Cervical fistula
Canal that opens into tonsillar sinus and external side of neck due to persistence of parts of 2nd groove and pouch
