Pharyngeal Arches Flashcards
What does our pharyngeal apparatus consist of?
Phargyngeal arches, pouches, grooves, clefts and membranes. They will make our. nasal cavities, mouth, larynx, pharynx and neck
Describe the relationship between pharyngeal cleft, pharyngeal arch and pharyngeal pouch.
Clefts (aka Grooves) are the ectodermal structures on the external surface of the pharyngeal arches.
Arches are the structures themselves, which give rise to an artery, a cartilage part, a muscular part, and a nervous part.
Pouches are the endodermal internal surface of the arch.
How do the pharyngeal arches develop
Early in week 4: NCC migrate to the future head and neck. Arches 1 and 2 develop at the same time. 1st pair of arches (primordial jaw) appear as elevations lateral to the pharynx Arches 2-4 appear as ridges on each side of the future neck and head. 5/6 are rudimentary: we cannot see them on the surface of the embryo. 5th arch may not develop
What does each arch. consist of?
Core. of mesenchyme (mesoderm and NCC) covered. externally. by ectoderm and internally. by. endoderm.
First arch separates into what?
maxillary. and mandibular prominence.
Week 5: PA2 overgrows PA3/4 -> forms cervical sinus (a depression of ectoderm) End of 7 week: cervical sinus diappears
What are the general roles of the NCC, the paraxial mesoderm, the lateral plate mesoderm, and the pharyngeal endoderm in the developing pharyngeal arches?
Neural crest cells: make the maxillary and mandibular prominences, as well as the CT, bone, skin, and smooth muscle.
Paraxial mesoderm is called the myogenic mesoderm, because it forms the muscle primordium in each arch.
Lateral plate mesoderm gives rise to angioblasts which form endothelium.
Pharyngeal endoderm plays a regulatory role
What does a typical pharyngeal arch consist of?
- An artery arises from truncus arteriosus of the primordial heart: goes around primordial pharynx -> dorsal aorta 2. Cartilaginous rod makes the makes the skeleton of the arch. 3. Muscular component becomes the muscles in the head and neck. Sensory. and motor nerves will supply the mucosa and muscles that come from each arch. Nerves are made in the brain and grow in to the arch.
What muscles come from the first arch?
What cranial nerve innervates them?
Muscles of mastication.
CN V (only maxillary and mandibular division)
- sensory for head and neck
- motor for mastication muscles
What muscles come from the second arch? What cranial nerve innervates them?
Stapedius and the muscles of facial expression.
CN VII
- Motor for #smileandsaycheese
What muscle comes from the third arch?
What cranial nerve innervates it?
elevateanddilate
Stylopharyngeus M
CN 9 (IX)
What muscles come from the fourth arch?
What cranial nerve innervates them?
pushitpushitrealgood
Cricothyroid, levator veli palatini and the constrictors of the pharynx.
CN X’
- 4th: superior laryngeal branch of CN X and its recurrent laryngeal N
What muscles come from the sixth arch?
What cranial nerve innervates them?
Intrinsic muscles of the larynx.
CN X
#soundoff
In the second arch, the muscles of facial expression come from_________, and the superior (ocular) muscles come from the __________.
paraxial mesoderm
prechordal mesoderm
What is Meckel’s cartilage?
What is it’s function?
The cartilage of pharyngeal arch 1.
Used as a model for osteoblasts to form the mandible. After the mandible is created, Meckel’s cartilgae will degenerate.
Also, two dorsal nodules break off and serve as a precursor from the malleus and incus.
What is formed from the perichondrium of Meckel’s cartilage?
- Anterior ligament of the malleus.
- Sphenomandibular ligament.
Both the malleus and incus are from
NCC
What forms the stylohyoid ligament?
Riechert’s cartilage from PA 2.
Where does Riechert’s cartilage come from, and what does it make?
Riechert’s cartilage comes from pharyngeal arch 2, and makes the stapes and styloid process of the temporal bone.
It also makes the lesser cornu of the hyoid, and the ligament in between its structures - the s_tylohyoid ligament._
What is formed by the cartilage of the third pharyngeal arch?
Greater cornu of the hyoid bone.
What forms the body of the hyoid bone?
Hypopharyngeal eminence (from PA 3 and PA 4)
What is formed by the fourth and sixth arch cartilages?
Laryngeal cartilages.
What forms the lesser cornu, greater cornu, and body of the hyoid?
Lesser cornu = Reichert’s cartilage (PA 2)
Greater Cornu = Third arch cartilage
Body of Hyoid = Hypopharyngeal eminence (PA 3 and PA 4)
- Distinguish between the neural crest and paraxial derived components of the
pharyngeal arches.
Muscles of the pharyngeal arches come from paraxial and prechordal mesoderm mesoderm.
The endothelium of the lateral plate come from lateral plate mesoderm.
Pharyngeal arch cartilages are neural crest derived.
Our primordial pharynx is derived from what>
foregut
how do we separate the pouches from the groove?
- Pouch endoderm contacts ectoderm on the pharyngeal groove -> mesenchyme enters ->forms a double-layered pharyngeal membrane, which separates the pouches from the groove
What is formed from the 1st pharyngeal membrane + intervening mesenchyme
Tympanic membrane
What all is derived from the first pharyngeal pouch?
ENDODERM THAT LINES THE POUCHES FORMS THE IMPORTANT ORGANS IN
UR HEAD AND NECK
Forms the tubotympanic recess.
This recess becomes both the pharyngotympanic tube (distally) as well as the tympanic cavity, the mastoid antrum, and a contribution to the tympanic membrane (proximally).
What all is derived from the second pharyngeal pouch?
Plargely obliterase as we make the palatine. tonsil.
art of the cavity of the pouch forms the tonsillar sinus.
Endoderm of the pouch proliferates and breaks down, forming the tonsillar crypts in the center, and the epithelium of the tonsils and crypts on the outside.
Mesenchyme around pouch forms lymphoid tissue and will organize into lymphatic nodules of the palantine tonsil.
what is all derived from our 3rd pouch
seperate into dorsal and ventral bulbar parts/
epithelium of dorsal bulbar part bcomes inferior parathyroid gland.
Epithelium from ventral part proliferates -> obliterates the cavities
- > parts come together
- > form thymus
What all is derived from the fourth pharyngeal pouch?
This forms a dorsal bulbar part and a ventral hollow part (just like arch 3).
The dorsal part becomes the superior parathyroid gland (not to be confused by the more superior pouch number 3 forming the inferior parathyroid gland).
The hollow part becomes the ultimopharyngeal body, which fuses with the thyroid gland and disseminates to form the parafollicular cells.
What are our pharyngeal grooves?
arise during week 4/5
separate pharyngeal arches externally
1st pair: the dorsal part of the 1st pharyngeal groove persists as the meatal plug. The meatal plug degenerates to form the internal portion of the external acoustic meatus.
Pharyngeal grooves 2-4 lie in cervical sinus and obliterate when the neck develops
birth defects of what pharyngeal groove are the most common
2nd
cervical (branchial) cysts
An opening behind the mandible created by the failure of the second pharyngeal groove (of the cervical sinus) to close completely.
They are typically asymptomatid until they get larger and fill with fluid and cellular debris.
thyroid gland deveopment
Where does the ultimopharyngeal body come from?
What is its function?
The ultimopharyngeal body comes from the ventral part of the 4th pharyngeal pouch. Endoderm)
It fuses with the thyroid gland and disseminates, forming the parafollicular (C Cells) of the Thyroid (which produce calcitonin).
what is first pharyngeal arch syndrome
abnormal development of the components of the first arch: causing malformations in EYES, EARS, MANDIBLE AND PALATE/
D/t insuffcient migration of NCC into 1st arch at week 4
examples of 1st pharngeal arch syndrome
- Treacher Collins Syndrome (mandibulofascial dysotasis)
- Pierre Robin Sequence
What is Treacher-Collins syndrome?
What is the cause?
(Mandibulofacial dysostosis)
Treacher-Collins syndrome (mandibulofacial dysostosis)
• Malar hypoplasia w/ down-slanting palpebral fissures, defects
of lower eyelids, deformed external ears, & sometimes middle
& internal ears
• Autosomal dominant disorder; mutations in Treacher Collins–
Franceschetti syndrome 1 gene (TCOF1)
• Encodes for the protein TREACLE, involved in ribosome
biogenesis
• Truncated in TCS leading to ↑↑ apoptosis of cranial NCC
What is the Pierre Robin sequence?
Pierre Robin sequence:
• Typically occurs de novo in most patients
• Associated with hypoplasia of the mandible, cleft
palate, & defects of the eyes & ears
• Initiating defect is a small mandible
(micrognathia) → results in posterior
displacement of the tongue → obstruction of full
closure of the palate → results bilateral cleft
palate
PRS = Palate (cleft), Retracted Tongue, Small mandible
other congenital abnormalities
agenesis of thyroid gland/thyroid hemiagenesis
DiGeorge
agenesis of thymus and parathyroid glands -> congenital hypoPARATH
