Development of the Pharyngeal Apparatus Flashcards
What makes up the pharyngeal apparatus?
pharyngeal arches, pouches, grooves, and membranes
When do the pharyngeal arches develop?
early in the 4th week
What is the first pair of arches known as?
the primordial jaws
What initiates the formation of the pharyngeal arches?
NCCs migrate away from the dorsal aspect of the developing neural tube and begin to populate ventral areas in what will be the head and neck
Where do cranial neural crest cells migrate from?
forebrain, midbrain, and hindbrain regions in the developing neural tube
what are the three main components of the pharyngeal arches?
core, external lining, internal lining
what is the core of the pharyngeal arches composed of?
mesoderm and mesenchyme
what is the external lining of the pharyngeal arch composed of?
ectoderm
what is the internal lining of the pharyngeal arch composed of?
endoderm
What is mesenchyme
embryonic CT
where does the mesoderm in the core of the pharyngeal arch come from?
it arises from paraxial mesoderm
what does the NCC-derived mesenchyme in the pharyngeal arch form?
all connective tissue in the head, including the dermis and smooth muscle
what does the paraxial mesoderm in the pharyngeal arch form?
forms PA musculature
what does the lateral plate mesoderm in the PA form?
angioblasts that differentiate into endothelium
what does prechordal plate mesoderm in the PA form?
extraocular musculature
What is the cartilage of the first pharyngeal arch also known as?
Meckle’s cartilage
what does the dorsal part of meckle’s cartilage form?
malleus and the incus
what does the ventral part of meckle’s cartilage form?
primordium of the mandible (like a place holder)
what does the perichondrium of meckle’s cartilage form?
anterior ligament of the malleus and the sphenomandibular ligament
what is the cartilage of the 2nd pharyngeal arch also known as?
riechert’s cartilage
what does the dorsal part of riechert’s cartilage form?
stapes and styloid process o the temporal bone
what does the perichondrium of riechert’s cartilage form?
the styloidhyoid ligament
what does the ventral portion of riechert’s cartilage form?
It ossifies to form the lesser cornu/horn of the hyoid bone
What does the third pharyngeal arch cartilage form?
it ossifies to form the greater cornu/horn of the hyoid bone
what is the body of the hyoid bone formed by?
the hypopharyngeal eminence
what does the cartilage of the 4th pharyngeal arch form?
laryngeal cartilages including the epiglottis
what does the cartilage of the 6th pharyngeal arch form?
laryngeal cartilages
Most muscular components of the face arise from what?
paraxial mesoderm
the first pharyngeal arch gives rise to what musculature?
muscles of mastication, mylohyoid, anterior belly of the digastric, tensor veli palatini, and tensor tympani
the second pharyngeal arch gives rise to what musculature?
stapedius and muscles of facial expression
the third pharyngeal arch gives rise to what musculature?
the stylopharyngeus
the fourth pharyngeal arch gives rise to what musculature?
cricothyroid and pharyngeal constrictors
the sixth pharyngeal arch gives rise to what musculature?
intrinsic muscles of the larynx
where do the extraocular muscles arise from?
the prechordal plate
where does the tongue musculature arise from?
the occipital myotomes
what nerve supplies the first pharyngeal arch?
trigeminal (maxillary and mandibular divisions)
what nerve supplies the second pharyngeal arch?
facial
what nerve supplies the third pharyngeal arch?
glossopharyngeal
what nerve supplies the 4-6th pharyngeal arch?
vagus
what are the general signs of a first arch syndrome?
malformation of the eyes, ears, mandible, and palate
what causes a first arch syndrome?
insufficient migration of NCC into the 1st arch during the 4th week of development
what is another name for treacher-collins syndrome?
mandibulofacial dysostosis
what causes treacher-collins syndrome?
mutations in TCOF1 gene
what does TCOF1 encode for?
the protein TREACLE, which is involved in ribosome biogenesis
what happens if the TREACLE protein is truncated?
there is increased apoptosis of cranial NCCs
what is pierre robin sequence associated with?
hypoplasia of the mandible, cleft palate, and defects of the eyes and ears
what is the initiating defect of pierre robin sequence?
small mandible (micrognathia)
where are pharyngeal grooves located?
externally between pharyngeal arches (covered with ectoderm)
where are pharyngeal pouches located?
internally as part of the pharynx (covered with endoderm)
what does the first pharyngeal groove form?
the external acoustic meatus
where do grooves 2-4 lie?
in the cervical sinus
what does the first pharyngeal pouch become?
it expands into the tubotympanic recess, which becomes the tympanic cavity and mastoid antrum
the tubotympanic recess will eventually elongate into what?
the pharyngotympanic tube (auditory tube)
what forms the tympanic membrane?
the 1st pharyngeal membrane + the intervening mesenchyme
what does the second pouch form?
tonsillar sinus
what does the endoderm of the second sinus form?
tonsillar epithelium
what does mesenchyme from the second pouch form?
lymphoid nodules of palatine tonsil
what does the dorsal part of the third pouch become?
inferior parathyroid gland
what does the ventral part of the third pouch become?
thymus
where does the third pouch migrate to?
caudally (due to growth of brain and cardiac regions)
what does the dorsal part of the 4th pouch become?
superior parathyroid gland
what does the remainder of the 4th pouch become?
an ultimobranchial body
what happens to the ultimobranchial body?
it fuses with the thyroid gland and gives rise to the parafollicular cells
how is an external cervical sinus detected?
due to discharge of mucus
what is an external cervical sinus commonly associated with?
auricular sinuses
when does the thyroid gland (thyroid primordium) develop?
around day 24 of development
what does the thyroid primordium form from?
an endodermal thickening in the floor of the primordial pharynx
how is the thyroid gland connected to the tongue?
by a narrow tube known as the thyroglossal duct
When will the thyroid primordium become its definitive shape/ when will the thyroglossal duct degenerate?
week 7
what is mesenchyme derived from?
migratory NCCs
What kind of mesoderm is located in the core of the pharyngeal arch?
paraxial mesoderm (largest contributor), lateral plate mesoderm, and prechordal plate mesoderm
What is the hypopharyngeal eminence?
a prominence in the floor of the embryonic pharynx (from PA3 and PA4)
obstruction of full closure of the palate due to micrognathia leads to what?
bilateral cleft palate
what is an external cervical sinus?
failure of the 2nd groove and cervical sinus to obliterate
what is an internal cervical sinus?
ingrowth of the 2nd pouch
what are remnants of the cervical sinus and/or 2nd groove that get covered with skin?
cervical cysts
What does an internal cervical sinus open into?
tonsillar sinus
what is it called when the second pouch remains open out to the second groove and then there is leakage of fluid and other substances that pass through the external opening of the skin?
cervical fistula
what is it called when the thyroid gland develops but does not descend?
sublingual thyroid gland
what is DiGeorge syndrome?
a breakdown of signaling from PA endoderm to NCC
what is not formed in digeorge syndrome?
thymus and parathyroid gland
