Embryology of Pharyngeal Arches Flashcards
What pharyngeal arch do the primordial jaws arise from?
1st PA
PA1 receives NCC from what rhombomere?
R1-2
PA2 receives NCC from what rhombomere?
R4
PA 3/4 receive NCC from what rhombomere?
R6-7
Rhombomeres arise from what part of the brain?
Hindbrain
At what gestational age does the cervical sinus form? When does it disappear?
5th week to 7th week
The normal formation of the cervical sinus is the result of what?
PA2 overgrowth of PA3/4 => Formation of an ectodermal depression
What structures will a typical pharyngeal arch contain?
Artery - from truncus arteriosus
Cartilagenous rod - skeleton
Muscular component
Sensory/Motor nerves
What does the dorsal part of Meckel’s cartilage form?
Malleus and Incus bones
What does the ventral side of Meckel’s cartilage give rise to?
Primordium of mandible, will be overgrown by osteogenic cells
What does the perichondrium of Meckel’s cartilage form?
Anterior ligament of Malleus bone and sphenomandibular L.
What PA does Meckel’s cartilage arise from?
PA1
What is the cartilage of PA2?
Riechert’s cartilage
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 PA cartilage do the stapes and the styloid process of the temporal bone arise from?
Riechert’s cartilage from 2nd PA
What does the 3rd PA 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 PA3 and PA4
What PA do the laryngeal cartilages come from?
PA 4 and 6 (except epiglottis)
What muscle does the 3rd PA give rise to?
Stylopharyngeus M.
What muscles do the 4th PA give rise to?
Cricothyroid M.
Levator veli palatini M.
Pharyngeal constrictor ms.
What PA gives rise to the intrinsic muscles of the larynx?
6th PA
What type of cranial nerve supply muscles derived from the arches? Skin and mucous membranes?
Muscles - SVE
Skin and mucous membranes - SVA
What initiates formation of double-layered pharyngeal membranes?
Pouch endoderm contacts ectoderm of pharyngeal grooves
Around week 20, mesenchyme of the 2nd pharyngeal pouch will differentiate into what tissue?
Lymphoid tissue
What is the direct embryonic origin of the inferior parathyroid gland?
Epithelium of Dorsal bulbar portion of 3rd PA
What is the direct embryonic origin of the superior parathyroid gland?
Epithelium of dorsal bulbar portion of 4th PA
In what week are the parathyroid glands formed?
Week 6
What PA is a cervical/branchial cyst most likely to be a remnant of?
PA 2
In what week are pharyngeal grooves 2-4 obliterated?
Week 7
What is the direct embryological origin of the foramen cecum?
Thyroglossal duct
What structure connects the fetal tongue to the developing thyroid gland?
Thyroglossal duct
What week do thyroid follicles form?
Week 10
A pt with a pyramidal lobe of the thyroid most likely had abnormal thyroid gland development in what week?
Week 7
What week of thyroid development does colloid appear and TH synthesis begin?
Week 11
What week do fetal TSH and thyroxine reach adult levels?
35 weeks?
What is the direct embryonic origin of the ultimopharyngeal body?
Ventral part of the 4th pouch (NCC)
What does the ultimopharyngeal body give rise to?
Parafollicular cells (fuses with thyroid gland and disseminates)
Abnormal migration of NCC into the 1st pharyngeal arch can cause what facial features to be malformed?
Eyes, ears, mandible, palate
Mutation in the what gene causes Treacher-Collin’s sydrome? What does the mutation result in?
TCOF1
Cannot make TREACLE ptn, involved in ribosome biogenesis, leads to increased apoptosis of cranial NCCs
What autosomal dominant disorder leads to malar hypoplasia, deformed external ears and down-slanting palpebral fissures?
Treacher Collins syndrome (Mandibulofacial dysostosis)
What is the Pierre Robin Sequence?
- 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
Which lobe is more commonly absent in thyroid hemiagenesis?
L 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
