9: Development Of The Pharyngeal Apparatus

Question 1

When do PAs start developing?

Answer 1

Early 4th week

Question 2

What starts the development of pharyngeal arches?

Answer 2

NCCs migrate into future head and neck

Question 3

What is the 1st pair of pharyngeal arches referred to as?

Answer 3

The primordial jaw

Question 4

Core of each PA

Answer 4

Mesoderm + mesenchyme

Question 5

Where is mesenchyme derived from?

Answer 5

Migratory NCCs (NCCs from neural tube forebrain, midbrain, and hindbrain)

Question 6

What forms all CT in the head, including dermis and smooth muscle?

Answer 6

Mesenchyme

Question 7

Head mesoderm is derived from what type of mesoderm?

Answer 7

Paraxial mesoderm

Question 8

What does lateral plate mesoderm form in the head?

Answer 8

Endothelium

Question 9

What does prechordal plate mesoderm form in the head?

Answer 9

Extraocular musculature

Question 10

What covered PAs externally and internally?

Answer 10

Ectoderm and endoderm

Question 11

Two functions of PAs

Answer 11

1. Support lateral walls of primitive pharynx

2. Give rise to facial prominences for craniofacial development

Question 12

Other name for 1st and 2nd PA cartilages

Answer 12

1st cartilage: Meckel’s cartilage

2nd cartilage: Reichert’s cartilage

Question 13

What forms the body of the hyoid?

Answer 13

Hypopharyngeal eminence, which forms from PA3 and PA4

Question 14

Specific nerves supplying 4th and 6th PA

Answer 14

4th: recurrent laryngeal branches, superior laryngeal N
6th: recurrent laryngeal branches

Question 15

Which is internal vs external, grooves and pouches

Answer 15

Grooves: external
Pouches: internal

Question 16

What does the 1st groove form?

Answer 16

External acoustic meatus

Question 17

Where are grooves 2-4?

Answer 17

In the cervical sinus

Question 18

Development of groove 2

Answer 18

Grows inferiorly to cover cervical sinus (birth defects can occur with this)

Question 19

What causes First Arch Syndrome?

Answer 19

Insufficient migration of NCCs into first arch

Question 20

What can be malformed in First Arch Syndrome?

Answer 20

Eyes, ears, mandible, palate

Question 21

Two syndromes involved in First Arch Syndrome

Answer 21

1. Treacher-Collins Syndrome

2. Pierre Robin Sequence

Question 22

Treacher Collins Syndrome (mandibulofacial dystostosis): S/S

Answer 22

Malar hypoplasia, downward slanting palpebral fissures, defects in lower eyelids, deformed external ears (sometimes internal too)

Question 23

Genetics of Treacher-Collins Syndrome

Answer 23

Mutation in TCOF1 gene (TREACLE protein); is autosomal dominant

Question 24

What happens with a TCOF1 mutation?

Answer 24

Ribosome biogenesis is truncated -> increased apoptosis of cranial NCCs

Question 25

Pierre Robin Sequence

Answer 25

Hypoplasia of mandible, cleft palate, defects in ears and eyes

Question 26

Genetics of Pierre robin sequence

Answer 26

De novo typically

Question 27

Initiating defect of Pierre Robin Sequence and the cascade of things that occur from there

Answer 27

1. Micrognathia 2. Posterior displacement of tongue 3. Obstruction of full closure of palate 4. Bilateral cleft palate

Question 28

External cervical sinus

Answer 28

Failure of 2nd groove and cervical sinus to obliterate

Question 29

How is external cervical sinus detected?

Answer 29

Discharge of mucus

Question 30

Internal cervical sinus

Answer 30

Persistence of 2nd pouch, opens into tonsillar sinus or near palatopharyngeal arch

Question 31

Cervical cysts

Answer 31

Remnants of cervical sinus and/or 2nd groove -> slowly enlarging painless cyst in neck

Question 32

Cervical fistula

Answer 32

Canal that opens into tonsillar sinus and external side of neck due to persistence of parts of 2nd groove and pouch