Development of the Pharyngeal Apparatus

Question 1

When do NCCs migrate into the future head and neck?

Answer 1

Early 4th week

Question 2

What are the first pair of arches called?

Answer 2

Primordial jaws

Question 3

What are rhombomeres (R1-7)?

Answer 3

Divisions of hindbrain that contribute NCC into tje pharyngeal arches.

Question 4

Which rhombomeres contribute to which pharyngeal arches?

Answer 4

PA1 = R1-2
PA2 = R4
PA3/4 = R6/7

R3 and R5 don’t produce much NCC.

Question 5

What layers are in a pharyngeal arch?

Answer 5

Inner endoderm.
Mesenchyme core.
Outer ectoderm.

Question 6

1st arch gives rise to:

Answer 6

Maxillary and mandibular prominences

Question 7

2nd arch does what?

Answer 7

Overgrows PA3/PA4 and forms cervical sinus (occurs in week 5, and disappears week 7).

Question 8

What else does NCCs form?

Answer 8

CT, integument and smooth muscles.

Question 9

What kind of mesoderm migrates into each arch?

Answer 9

Paraxial mesoderm

Question 10

What are angioblasts from? What does it become?

Answer 10

From lateral plate mesoderm, and becomes endothelium.

Question 11

Each arch has what components? (4)

Answer 11

Artery
Cartilaginous rod
Muscular component
Nerves

Question 12

What do PA arteries arise from?

Answer 12

Truncus arteriosus

Question 13

What is Meckel’s cartilage?

Answer 13

The cartilage of PA1.

Question 14

What do dorsal parts of the Meckel’s cartilage become?

Answer 14

Dorsal parts break away and ossify to become malleus and incus.

Question 15

What do the anterior ligament of the malleus and sphenomandibular L. come from?

Answer 15

Perichondrium of Meckel’s cartilage (PA1).

Question 16

What does the ventral part of Meckel’s cartilage become?

Answer 16

The primordium of the mandible.

Question 17

What is Riechert’s cartilage?

Answer 17

Cartilage of PA2.

Question 18

What does the stapes come from?

Answer 18

Dorsal part of Riechert’s cartilage.

Question 19

What does the ventral end of Riechert’s cartilage become?

Answer 19

Lesser horn of the hyoid bone

Question 20

What does 3rd arch cartilage become?

Answer 20

It ossifies to form greater horn/cornu of hyoid

Question 21

What does hypopharyngeal eminence form?

Answer 21

Body of hyoid.

Question 22

What do the 4th and 6th PA cartilage form?

Answer 22

They form laryngeal cartilages (besides epiglottis).

Question 23

What happens to 5th arch cartilage?

Answer 23

Degenerates

Question 24

1st arch muscles:
2nd arch muscles:
3rd arch muscles:
4th arch muscles:
5th arch muscles:

Include innervation

Answer 24

1st: muscles of mastication. CN V.
2nd: stapedius m., ms. of facial expression. CN VII.
3rd: stylopharyngeus m. CN IX.
4th: cricothyroid m., levator veli palatini m. and pharyngeal constrictor ms. CN X.
6th: intrinsic ms. of larynx. CN X.

Question 25

SVE supply | SVA supply

Answer 25

SVE: muscles derived from arches. SVA: dermis and mucous membranes of head/neck.

Question 26

Which CN supplies PA1?

Answer 26

CN V

Question 27

Which CN supplies PA2?

Answer 27

CN VII

Question 28

Which CN supplies PA3?

Answer 28

CN IX

Question 29

Which CN supplies PA4-6?

Answer 29

CN X

Question 30

3rd arch arteries become: Dorsal aortae become: Common carotids become:

Answer 30

3rd arch arteries become: common and internal carotids. Dorsal aortae become: distal internal carotids. Common carotids become: create external carotids de novo.

Question 31

What makes primordial pharynx?

Answer 31

Foregut endoderm

Question 32

Pharyngeal clefts, pouches and membranes

Answer 32

Pharyngeal clefts are external. Pharyngeal pouches are internal. Pharyngeal membranes separate pouches from grooves.

Question 33

What does the 1st pharyngeal membrane become?

Answer 33

Tympanic membrane

Question 34

What does 1st pharyngeal pouch become?

Answer 34

Ear anatomy

Question 35

What does the 2nd pharyngeal pouch become?

Answer 35

Creates tonsillar sinus, tonsillar crypts (endoderm), lymphoid tissue (mesenchyme), lymphatic nodules.

Question 36

What does 3rd pharyngeal pouch become?

Answer 36

Inferior parathyroids and thymus.

Question 37

What does 4th pharyngeal pouch become?

Answer 37

Superior parathyroids

Question 38

What does 1st pharyngeal grooves become?

Answer 38

External acoustic meatus

Question 39

Where are grooves 2-4?

Answer 39

Lie in the cervical sinus

Question 40

Cervical (Branchial) Cysts

Answer 40

Remnants of cervical sinus (2nd groove) Lie free in neck, inferior to mandible. Accumulation of fluid/cellular debris from desquamation.

Question 41

How does thyroid form?

Answer 41

Primordial pharynx thickens and descends from tongue area and ventral to the laryngeal cartilage.

Question 42

Thyroglossal duct

Answer 42

Connects tongue to thyroid

Question 43

TH levels in: 11th wk 20th wk 35th wk

Answer 43

11th wk - colloid appears and TH synthesis occurs. 20th wk - fetal TSH and T3/4 increase. 35th wk - TSH and T3/4 are adult levels.

Question 44

What is the ultimopharyngeal body from? | What does it form?

Answer 44

``` From the ventral part of 4th pouch. Parafollicular cells (from NCC). ```

Question 45

Treacher-Collins syndrome (PA1 syndrome)

Answer 45

Deficits w/ downward slanting features, deformed, eyelids, external ears, sometimes middle and inner ears. Ribosomes do not function --> apoptosis of cranial NCC.

Question 46

Pierre Robin sequence (PA1 syndrome)

Answer 46

Associated w/ hypoplasia of mandible (micrognathia), cleft palate, eye/ear defects.

Question 47

Thyroid hemiagenesis

Answer 47

UL absence of thyroid (usually Left). | Mutations in receptor for TSH usually involved.

Question 48

DiGeorge syndrome

Answer 48

Agenesis of thyroid and parathyroid glands. Low PTH. Cardiac abnormalities, immune problems, etc.