Pharyngeal Apparatus Flashcards
What does the pharyngeal apparatus consist of?
Pharyngeal arches, grooves, pouches and membranes
Are the pharyngeal arches, grooves, pouches and membranes bilateral?
duh
When do the pharyngeal arches start to develop?
Early in the 4th week
What cell type migrates to form the pharyngeal arches?
NCC
What tissue types are within each arch?
Mesoderm and mesenchyme = middle
Ectoderm = external portion
Endoderm = internal portion
What does the endoderm in the arches do?
Regulates development of the arches
Describe the locations of the arches, grooves, membranes and pouches in relation to eachother
The arches make up the circular prominence and in between each arch is where you will find the grooves, pouches and membranes
- The Pouches are internal
- The grooves are external at the same level
- The Membranes are in between a pouch and a groove
What forms the mesoderm in the pharyngeal arch?
Paraxial mesoderm
What forms the mesenchyme in the pharyngeal arch?
NCC
What will the mesoderm in the pharyngeal arch become?
Musculature
What will the mesenchyme in the pharyngeal arch become?
Cartilage and bony elements, smooth muscle and dermis
What will the lateral plate mesoderm create?
Endothelium
What will the prechordal plate mesoderm create?
Extraocular muscles
What are the 4 elements that each pharyngeal arch consists of?
Cartilagenous rods
Muscular components
Cranial nerves
Arteries
What do the cartilagenous rods of an arch create?
Form skeletal elements
What do the muscular components of an arch create?
Form head and neck musculature
What do the cranial nerves of an arch create?
Form sensory and motor components
Cartilage of PA1
Meckel’s cartilage
What does the dorsal, ventral and perichondrium portions of meckel’s cartilage create?
Dorsal - malleus and incus (ear bones)
Ventral - primordium of mandible
Perichondrium - anterior ligament of malleus and the sphenomandibular ligament
Where does the actual bony mandible form?
Lateral to the meckel’s cartilage and then the cartilage disintegrates
Cartilage of PA2
Riechert’s cartilage
What does the dorsal, ventral and perichondrium portions of Riechert’s cartilage create?
Dorsal - stapes and styloid process of temporal bone
Ventral - ossifies to form lesser horn of hyoid bone
Perichondrium - stylohyoid ligament
What does cartilage of PA3 create?
Greater horn of hyoid bone
What does cartilage of PA4 create?
Laryngeal cartilages and epiglottis (NCC derived)
What does cartilage of PA6 create?
Laryngeal cartilages
What forms the body of the hyoid bone?
Hypopharyngeal eminence
Where does most musculature originate from?
Paraxial mesoderm
What creates the extraocular muscles?
Prechordal plate mesoderm
What creates the tongue musculature?
Occipital myotomes
PA1 musculature
Muscles of mastication (temporalis, massater, medial and lateral pterygoids)
PA2 musculature
Muscles of facial expression and stapedius
occipitofrontalis, platysma, orbicularis oculi and oris, zygomaticus major and minor, buccinator
PA3 musculature
Stylopharyngeus
PA4 musculature
Cricothyroid and phayrngeal constrictors (superior, middle and inferior)
PA6 musculature
Intrinsic laryngeal muscles
What nerve supplies PA1?
Trigeminal – V2 and V3 (sensory and motor)
What nerve supplies PA2?
Facial – CN VII (motor)
What nerve supplies PA3?
Glossopharyngeal – CN IX (motor)
What nerve supplies PA4 and PA6?
Vagus – CN X
What nerves specifically supply PA4?
Superior laryngeal and recurrent laryngeal branches
What nerve specifically supplies PA6?
Recurrent laryngeal branches
What causes first arch syndromes?
Insufficient NCC migration during the 4th week of development
What are the first arch syndromes?
Treacher-collins syndrome and Pierre-Robin sequence
How is Treacher-Collins syndrome inherited?
Autosomal dominant
What mutation causes Treacher-Collins syndrome?
Mutation in TCOF1 gene that results in decreased TREACLE protein which results in increased apoptosis of NCC!!
Symptoms of Treacher-Collins syndrome?
Malar hypoplasia, downward slanting palpebral fissures, external, middle and internal ear deformations
How is Pierre-Robin sequence inherited?
De novo
Describe the Pierre-Robin sequence
Initial defect = small mandible (micrognathia)
- Posterior displacement of tongue
- Palate unable to fully close
- BILATERAL CLEFT PALATE
What is the final result of Pierre-Robin sequence?
bilateral cleft palate (and probs micrognathia)
Where does the 1st groove/pouch lie?
Between the 1st and 2nd pharyngeal arches
What does the 1st groove create?
External acoustic meatus
What does the 1st pouch create?
Tubotympanic recess - - tympanic cavity and mastoid antrum
What is created when the endoderm over the 1st pouch extends to the 1st groove?
Tympanic membrane is created
What does the 1st membrane contribute to?
Tympanic membrane
What happens to the grooves 2-4?
Overgrowth of the 2nd arch creates a cervical sinus that houses grooves 2-4; the cervical sinus is eventually filled with mesenchyme from PA2 and it will be obliterated along with grooves 2-4 = bye bye
What does the 2nd pouch create?
Tonsilar sinus, tonsilar epithelium, lymphoid nodules of palatine tonsils
What creates lymphoid nodules of palatine tonsils from the 2nd pouch?
Mesenchyme
What does the dorsal and ventral portion of the 3rd pouch create?
Dorsal – inferior parathyroid gland
Ventral – thymus
Where do the dorsal and ventral portions of the 3rd pouch go?
Migrate caudally
What does the dorsal portion of the 4th pouch create?
Superior parathyroid gland
What does the ultimobranchial body of the 4th pouch do?
Fuses with thyroid gland to create parafollicular cells
What are the branchial anomalies?
External and internal cervical sinus, cervical cysts, cervical fistula
Failure of 2nd groove and cervical sinus to obliterate and detected due to discharge of mucus
External cervical sinus
Persistence of 2nd pouch that opens into tonsilar sinus
Internal cervical sinus
Rememnants of cervical sinus and/or 2nd groove that includes slow growing, painless cysts in the neck below the mandible filled with fluid and cell debris
Cervical cysts
Persistence of parts of 2nd groove and pouch that creates a canal that opens into tonsilar sinus and external side of neck
Cervical fistula
What all does a cervical fistula pass through?
Subcutaneous neck tissue, platysma, carotid sheath and tonsilar sinus
When does the thyroid gland begin to develop?
24 days post fertilization
Where does the thyroid gland move?
Descends into neck as tongue grows, anteriorly to hyoid bone and laryngeal cartilages
What connects tongue to thyroid gland?
Thyroglossal duct - eventually disintegrates
Any thyroid tissue (functional) not in correct place
Ectopic thyroid tissue
Thyroid gland forms but does not descend
Sublingual thyroid gland
Can form in the tongue or neck, make sure it is not a functional thyroid gland (ectopic)
Thyroglossal duct cyst
Which lobe is more commonly absent with thyroid hemiagenesis?
Left lobe
What causes DiGeorge syndrome?
Breakdown of signaling from PA endoderm to NCC
What symptoms can DiGeorge syndrome cause?
Agenesis of thymus and parathyroid glands, congenital hypoparathyroidism, cardiac abnormalities and shortened upper lip and nasal clefts
