pharyngeal arches Flashcards
what do pharyngeal arches contribute to?
formation of nasal cavities, oral cavitiy, tongue, larynx, pharynx, ear and neck.
when do the pharyngeal arches begin to develop?
4th week as neural crest cells begin to migrate towards the future head and neck region
what is the first set of pharangeal arches
the premordial jaw- they appear lateral to developing pharynx
what sets of pharangeal arches contribute to the head and neck regions?
arches 2-4
which sets of ph.arches are rudimentary or not visible on surface of embryo?
5-6
what composes the ph. arch core
meso derm ( head mesoderm dervived from paraxial mesoderm) and mesenchyme (embryonic CT derived form migratory neural crest cells)
what germ layer covers the ph. arch
ectoderm
what germ layer internally lines the pharyngeal arch?
endoderm
once formed, the pharangeal arches carry out what function?
support the lateral walls of the primitive pharynx, and give rise to facial prominences that contribute to craniofacial development
specifically what does NCC derived mesenchyme contribute to?
forms all CT in the head, including the dermis and smooth muscle
what does the paraxial mesoderm contribute to?
populates each arch to form PA musculature
what does the lateral plate mesoderm contribute to
angioblasts differentiate into endothelium
what does the prechordal plate mesoderm contribute to
extraocular musculature
what does the cartilagenous rod form?
skeletal elements
what does the muscular component form
muscles of the head and neck
what do the cranial nerves form
sensory and motor components
what does the arch artery form
vasculature of the head and neck
describe Meckel’s cartilage
cartilage for Arch 1
dorsal portion will form malleus and incus
perichondium –> anterior ligament of malleus and sphenomandibular llgament
ventral parts–>primordium of the mandible
bone forms laterally to mer
arch artery for PA1
terminal branch of maxillary artery
arch artery for PA2
stapedial artery (embryonic), caroticotympanic artery (adult)
arch artery for PA3
common carotid artery, root of internal carotid
arch artery for PA4
arch of aorta (left side); right subclavian artery (right side), original sprouts of pulmonary arteries
arch artery for PA6
ductus arteriosus, roots of definitive pulmonary arteries
PA1 cranial nerve
maxillary and mandibular divisions of trigeminal nerve (V), ***ophthalmic division does not supply any arch components
PA2 cranial nerve
facial nerve (VII)
PA3 cranial nerve
glossopharyngeal (IX)
PA4/6 cranial nerve
vagus (X)
4th - superior laryngeal and recurrent branch of vagus n.
6th - recurrent laryngeal branch of vagus n.
where does the epiglottis come from?
neural crest cell derived
What is the cartilage for PA2
Reichert’s cartilage: dorsal region contributes to stapes and styloid process of the temporal bone, remainder desintegrates; perichondrium –>stylohyoid ligament; ventral end ossifies–> forms lesser cornu/ horn
third arch cartilage
ossifies–> forms greater cornu of hyoid bone; body of the hyoid bone is formed by hypopharyngeal eminence - prominence in floor of embryonic pharynx (PA3 and PA4)
what type of ossification does the mandible go through?
membranous ossification- does not use a cartilage model that is why meckel’s cartilage desintegrates before then.
4th arch cartilage
laryngeal cartilages including epiglottis (NCC derived)
6th arch cartilage
laryngeal cartilage, but origin is uncertain
first arch musculature
muscles of mastication (temporalis, masseter, medial and lateral pterygoids) ; mylohyoid, anterior belly of the digastric, tensor tympani, tensor tympani, tensor veli palatini (originate from head mesoderm)
first arch ligaments
anterior ligament of malleus, spheno-mandibular ligament
second arch cartilage
stapes, styloid process, lesser horns and part of body of hyoid (derived from the second-arch [Reichert’s] cartilage; originate from NCCs) stylohyoid ligament
second arch musculature
stapedius and muscles of facial expression (buccinator, auricular muscles, occipitofrontalis, posterior belly of digastric, stylohyoid,
third arch musculature
stylopharyngeus m.
fourth arch cartilage
thyroid and epiglottal laryngeal cartilages (derived from the 4th arch cartilage; originate from NCCs)
sixth arch cartilage
remaining laryngeal cartilages (derived form the 6th arch cartilage; uncertain whether they originate from Neural crest or mesoderm)
where do the extraocular muscles arise from?
prechordal plate
what is the innervation of the extraoccular muscles
SO(4) LR(6) remainder (3)
superior oblique - IV
lateral rectus- VI
levator palpebrae superioris; superior, medial and inferior recti; inferior oblique - III
where does the tongue musculature arise from?
tongue itself is from the pharyngeal arches but the associated musculature comes from the occipital myotomes (superiormost segments of the paraxial mesoderm, different from the unsegmented paraxial mesoderm that populates the rest of the arches, cervical, thoracic, lumbar, and saccrococcygeal myotomes)
4th arch musculature
cricothyroid, inferior pharyngeal constrictor
6th arch musculature
intrinsic laryngeal muscles (except cricothyroid)
first arch syndrome (umbrella term)
malformation of eyes, ears, mandible, and plate, which together constitute 1st arch syndrome
results from insufficient migration of NCC into the 1st arch during 4th week
which arch is the biggest arch?
first arch
treacher-collins syndrome (mandibulofacial dysostosis) - first arch syndrome
malar hypoplasia with down-slanting palpebral fissures, defects of lower eyelids, deformed external ears, and sometimes middle and internal ears
autosomal dominant; mutations in Treacher Collins-Franceschetti syndrome 1 gene (TCOF1)
what does the protein TCOF1 do?
encodes for the protein TREACLE, involved in ribosome biogenesis (impairs protein synthesis); truncates in TCS leading to increase in apoptosis of cranial NCC
pierre robin syndrome
typically de novo; associated with hypoplasia of the mandible, cleft palate and defects of the eyes and ears; initiating defect is a small mandible (micrognathia)–> results in posterior displacement of the tongue–> obstruction of full closure of the palate–> results in bilateral cleft palate
grooves are covered with…
ectoderm
pouches are covered with…
endoderm
1st groove will form the…
external acoustic meatus
which grooves lie within the cervical sinus
grooves 2-4
what does the 1st pouch turn into?
expands into tympanic recess–> tympanic cavity and mastoid antrum; elongates to form pharyngotympanic tube; endoderm contacts 1st pharyngeal groove –> contributes to tympanic membrane
what forms the tympanic membrane?
1st membrane and intervening mesenchyme
what does the 2nd pouch give rise to?
portion of tonsillar sinus; endoderm will form tonsillar epithelium; mesenchyme will form lymphoid nodules of palatine tonsil
what does the 3rd pouch give rise to?
dorsal portion differentiates into inferior parathyroid gland; ventral portions form the thymus; both migrate caudally due to growth of brain and cardiac regions
what does the 4th pouch give rise to?
drosal portion differentiates into superior parathyroid glands; ultimobranchial body –> fuses with thyroid gland and gives rise to parafollicular cells
parafollicular cells are… ()dermal in identity
endo-dermal
branchial anomalies: external cervical sinus (typical)
failure of 2nd groove and cervical sinus to obliterate- detected due to discharge of mucus; commonly associated with auricular sinuses
branchial anomalies: internal cervical sinus (rare)
persistence of 2nd pouch: opens into tonsillar sinus or near palatopharyngeal arch; ingrowth of the pouch, tonsillar tissue should fill in the pouch enough
branchial anomalies: cervical cyst
remnants of cervical sinus or 2nd groove; slowly enlarging, painless, free-lying cyst in the neck, inferior to angle of the mandible; accumulation of fluid and cellular debris
branchial anomalies: cervical fistula (most extreme)
canal that opens into tonsillar sinus and external side of the neck; persistence of parts of 2nd groove and pouch; ascends through subcutaneous tissue and platysma to reach carotid sheath; passes between carotids and opens into tonsillar sinus - fistula can be site of infection if pathogens pass through
what is the first endocrine gland to develop and when?
thyroid gland begins to develop approx. 24 dpf –> thyroid primordium
what gives rise to the thyroid gland?
forms from an endodermal thickening in floor of primordial pharynx
describe the migration of the thyroid gland
descends in the neck as tongue grows–> ventral to hyoid bone and laryngeal cartilages - held in place temporarily by the duct
what connects the thyroid gland and the tongue during development?
thyroglossal duct - will atrophy first then degenerate
describe the thyroid gland development from the promodium?
primordium is hollow, but will become solid, cellular mass; divides into R/L lobes connected by the isthmus; definitive shape by 7 weeks and thryroglossal duct will degenerate
thyroid gland anomalies: ectopic thyroid tissue
cervical , accessory and/or lingual can form along the course of the duct
thyroid gland anomalies: sublingual thyroid gland
forms correctly but does not descend in the neck
thyroid gland anomalies: thyroglossal duct cyst
form in tongue or anterior neck- critical to distinguish from ectopic thyroid prior to surgical removal
congenital anomalies: agenesis of thyroid gland
abscence of a thyroid gland or one of its lobes
congenital anomalies: thyroid hemiagenesis
unilateral failure of formation- left lobe is more commonly absent (mutations in the receptor for thyroid-stimulating hormone are likely involved)
congenital anomalies: Digeorge syndrome
breakdown of signaling from PA endoderm to NCC (chromosome deletion 22Q11); agenesis of thymus and parathyroid glands; congenital hypothyroidism; shortened philtrum of upper lip, low set and notched ears; nasal clefts, thyroid hypoplasia; cardiac abnormalities (defects of the aortic arch and heart)
