Lecture 6: Embryology of Pharyngeal Apparatus Flashcards
What does a pharyngeal apparatus consist of?
- Pharyngeal Arches
- Pharyngeal Pouches (internal structure - endoderm)
- Pharyngeal Grooves/Clefts (ectoderm)
What is the embryological origin of phayngreal arches?
Neural Crest Cells
What pharyngeal arch do the primordial jaws arise from?
1st Pharyngeal Arch
Neural Crest Cell
What germ layer(s) contribue to the core of a pharyngeal arch?
What germ layer(s) externally cover the pharyngeal arch?
- *Core:** Mesoderm and Mesenchyme (migratory NCC)
- *Cover:** Ectoderm and Endoderm
What is the function of pharyngeal arches?
- Support lateral walls of primordial pharynx
- Give rise to facial prominences of tissue that contribue to craniofacial development
What germ layer plays an essential role in regulation the development of arches?
Pharyngeal Endoderm
What germ layer gives rise to PA muscles?
Paraxial Mesoderm
What germ layer gives rise to endothelium?
Lateral Plate Mesoderm
What germ layer gives rise to extraocular muscles?
Prechordal Plate Mesoderm
What structures will a typical pharyngeal arch contain?
- Cartilagenous Rod: skeletal elements
- Muscular Component: Paraxial and Prechordal derived
- Cranial Nerves: sensory and/or motor components
- Artery: from truncus arteriosus
What pharyngeal arch does Meckel’s cartilage arise from?
Pharyngeal Arch 1
What does the dorsal part of Meckel’s cartilage form?
What germ layer do these structures arise from?
Malleus and Incus bones
Neural Crest Cells
What does the perichondrium of Meckel’s cartilage form?
Anterior ligament of Malleus bone
Sphenomandibular Ligament
What does the ventral side of Meckel’s cartilage give rise to?
Primordium of mandible (transient structure)
Proper mandible will form laterally to it while Meckel’s cartilage disintegrates
What is the cartilage of Pharyngeal Arch 2?
Riechert’s cartilage
What does the dorsal part of Riechert’s cartilage form?
Stapes
Styloid Process of the Temporal Bone
What arises from the ventral end of Riechert’s cartilage?
Lesser cornu/horn of Hyoid bone
What arises from the perichondrium of the Riechert’s cartilage?
Stylohyoid L.
What does the 3rd Pharnygeal cartilage give rise to?
Greater horn/cornu of hyoid bone
What does the hypopharyngeal eminence give rise to?
What PAs does it arise from?
Body of hyoid bone
Arises from Pharyngeal Arches 3 and 4: floor of embryonic pharanyx
What pharyngeal arches do the laryngeal cartilages come from?
Pharyngeal Arches 4 and 6
What pharyngeal arches do the epiglottis come from?
Pharyngeal Arch 4
Where does the aoritc arch system arise from?
Aortic Sac
What muscles does the 1<span>st</span> pharyngeal arch give rise to?
What is it innervated by?
Muscles of Mastication (4)
Cranial Nerve V3
What muscles do the 2nd pharygneal arch give rise to?
What is it innervated by?
- Stapedius
- Muscles of Facial Expression
Cranial Nerve VII
What muscle does the 3rd Pharyngeal Arch give rise to?
What is it innervated by?
Stylopharyngeus Muscle
Cranial Nerve IX
What muscles do the 4th pharygneal arch give rise to?
What is it innervated by?
- Cricothyroid M.
- Levator veli palatini M.
- Pharyngeal constrictor ms.
Cranial Nerve X
What muscles do the 6th pharygneal arch give rise to?
What is it innervated by?
Intrinsic Muscles of Larynx
Cranial Nerve X
What is the embryological origin of the External Acoustic Meatus?
1st Pharyngeal Groove
Ectoderm
What grooves lie in the cervical sinus?
Grooves 2-4
What is the fate of pharyngeal grooves 2-4?
Obliterated in Week 7
What part of the pharyngeal apparatus is a cervical/branchial cyst most likely to be a remnant of?
REMNANTS OF 2ND GROOVE/CERVICAL SINUS
- Slowly enlarging, painless, free-lying cyst in neck
- Inferior to MANDIBLE
- Accumulation of fluid and cellular debris
How does the cervical sinus remant develop?
2nd PA groove and cervical sinus fail to obliterate and are covered with skin
- Mucus discharge noted
- Typically bilateral
How does an Internal cervical sinus anomaly occur?
Persistence of 2nd PA pouch
- Opens into tonsillar sinus or near palatopharyngeal arch
- Rare
What initiates formation of double-layered pharyngeal membranes?
Pouch endoderm contacts ectoderm of pharyngeal grooves
What is the embryological origin of the Tympanic Membrane?
1st Pharyngeal Membrane
Mesenchyme
What structures are developed from 1<span>st</span> pharyngeal pouch?
- Tubotympanic Recess —-> Pharyngotympanic Tube
- Tympanic Cavity
- Mastoid Antrum
- Tympanic Membrane
What structures are developed from 2<span>nd</span> pharyngeal pouch?
Tonsillar Sinus
Around week 20, mesenchyme of the 2nd pharyngeal pouch will differentiate into what tissue?
Lymphoid tissue
What structures are developed from 3r<span>d</span> pharyngeal pouch?
Inferior Parathyroid Gland
Thymus (ventral portion)
What structures are developed from 4th pharyngeal pouch?
Superior Parathyroid Gland
Ultimobranchial body (NCC)
What does the ultimobranchial body give rise to?
Parafollicular cells
(fuses with thyroid gland and disseminates)
What is the origin of the thymus?
3rd Pharyngeal Pouch
endoderm
What is the origin of the thyroid gland?
Endodermal thickening of Primordial Pharnyx
What structure connects the fetal tongue to the developing thyroid gland?
Thyroglossal duct
Transient
What is the direct embryological origin of the foramen cecum?
Thyroglossal duct
Abnormal migration of NCC into the 1st pharyngeal arch can cause what facial features to be malformed?
Eyes, ears, mandible, palate
What autosomal dominant disorder leads to malar hypoplasia, deformed external ears and down-slanting palpebral fissures?
Treacher Collins syndrome (Mandibulofacial dysostosis)
Mutation in the what gene causes Treacher-Collin’s sydrome? What does the mutation result in?
TCOF1
Cannot make TREACLE protein, involved in ribosome biogenesis, leads to increased apoptosis of cranial NCCs
What is the Pierre Robin Sequence?
PA Arch 1 abnormality
- Small mandible (Micrognathia) =>
- Posterior displacement of the tongue => Obstruction of full closure of palate =>
- Bilateral cleft palate
Patients with Pierre Robin sequence likely had a defect in development of what embryonic structure?
1st PA
In thyroid hemiagenesis, what lobe is more commonly absent?
Left Lobe
A patient with agenesis of the thyroid and parathyroid glands, shortened philtrum of the upper lip, low-set ears, nasal cleft, and a heart murmur may have what disorder?
DiGeorge Syndrome
What is the pathology behind Digeorge Syndrome?
Breakdown of signaling from pharyngreal arch endoderm to Neural crest cells
