Development of Pharyngeal Arches Dennis

Question 1

When do the pharyngeal arches develop?

Answer 1

They develop in early 4th week as the NC cells migrate to the future head and neck

Question 2

What makes up the core of pharyngeal arches and what covers them externally/internally?

LO #1

Answer 2

Mesoderm and mesenchyme make up the core of each arch, ectoderm covers the arch externally, and endoderm covers the internal surface.

Question 3

LO #3

Where does the mesenchyme that makes up the core of the arch come from?

Answer 3

embryonic CT derived from migratory NCC

Question 4

LO #3

Where does the mesoderm of the head come from and what does it do for the arch?

Answer 4

Arises from paraxial mesoderm and gives each arch the ability to form PA muscles

Question 5

LO #3

How does the lateral plate mesoderm contribute to the pharyngeal arch?

Answer 5

angioblasts differentiate into endothelium

Question 6

LO #3

How does the prechordal plate mesoderm contribute to the pharyngeal arches?

Answer 6

extraocular muscles

Question 7

What plays an essential role in regulating development of arches??

Answer 7

pharyngeal endoderm

Question 8

What are the elements of pharyngeal arches?

Answer 8

1. cartiliaginous rods form skeleton
2. Muscular component
3. Cranial nerves
4. Arch artery

Question 9

LO #4,6

What cartilage makes up pharyngeal arch 1 and what does the dorsal part form?

Answer 9

Meckel’s Cartilage which will form the malleus and incus

Question 10

LO #4,6

What cartilage makes up the second pharyngeal arch and what does the dorsal region and ventral region form?

Answer 10

Riechert’s cartilage and the dorsal part will make the stapes and styloid process and the ventral portion will make the lesser horn of the hyoid

Question 11

LO #4,6

What happens to the third pharyngeal arch cartilage?

Answer 11

It ossifies forming the greater horn of the hyoid

Question 12

LO #4,6

What happens to the 4th and 6th arch cartilages?

Answer 12

4th forms laryngeal cartilages including epiglottis which is NCC derived

6th forms laryngeal cartialges also but origin is unknown

Question 13

What muscles and nerves are associated with the first arch?

Answer 13

Muscles of mastication and trigeminal

Question 14

What muscles and nerves are associated with the second arch?

Answer 14

Facial expression and stapedius Facial nerve

Question 15

What muscles and nerves are associated with the third arch?

Answer 15

stylopharyngeus CN 9 glossopharyngeal

Question 16

What muscles and nerves are associated with the fourth arch?

Answer 16

cricothyroid, pharyngeal constrictors and vagus nerve

Question 17

What muscles and nerves are associated with the sixth arch?

Answer 17

intrinsic muscles of larynx and vagus nerve

Question 18

What do the occipital myotomes give rise to?

Answer 18

tongue musculature

Question 19

What does the prechordal plate give rise to?

Answer 19

extraocular muscles

Question 20

What is Treacher Collins Syndrome?

Answer 20

First arch syndrome it is an autosomal dominant disorder with a mutation in the TCOF1 gene. Malar hypoplasia deformed ears and defectss of lower eyelids. Insufficient migration of NCC into 1 arch during the 4th week of development

Question 21

What is Pierre Robin sequence?

Answer 21

First arch syndrome. Occurs de novo in patients and is associated with hypoplasia of mandible cleft palate and defects of ears and eyes. Micrognathia is initiating defect which will result in displacement of the tongue obstructing closure of the palate resulting in bilateral clefft palate

Question 22

Where are pharyngeal grooves located and what are they covered with?

Answer 22

Externally between pharyngeal arches and covered with ectoderm

Question 23

Where are pharyngeal pouches lcoated and covered with?

Answer 23

Internally as part of pharynx and they are covered with endoderm

Question 24

What does the first groove form?

Answer 24

External acoustic meatus

Question 25

What does the first pouch form?

Answer 25

Tubotympanic recess and tympanic cavity and mastoid antrum. The pouch elongates to form pharyngotympanic tube. Contributes to the tympanic membrane

Question 26

what does the second pouch form?

Answer 26

Tonsillar sinus
Endoderm forms tonsillar epithelium
Mesenchyme forms lymphoid nodule of palatine tonsils

Question 27

What does the third pouch form?

Answer 27

inferior parathyroid gland from the dorsal portion

thymus from the ventral portion

Question 28

What does the fourth pouch form?

Answer 28

Dorsal part superior parathyroid glands

Ultimobranchial body fuses with thyroid gland and gives parafollicular cells

Question 29

What is the external cervical sinus?

Answer 29

It is an anomaly when the 2nd groove and cervical sinus do not obliterate. Detected due to discharge of mucus and commonly associated with auricular sinuses

Question 30

What is the Internal cervical sinus?

Answer 30

An anomaly, persistence of pouch two, it is rare and opens into tonsillar sinus or near palatopharyngeal arch

Question 31

What is a cervical cyst?

Answer 31

Remnant of cervical sinus and/or 2nd groove. Slowly enlarging painless, free lying cyst in the neck inferior to the angle of the mandible. Accumulates fluid and cellular debris

Question 32

What is a cervical fistula?

Answer 32

canal that opens into tonsillar sinus and external side of neck. It is a persistence of parts of the second groove and pouch. Ascends through the subcutaneous tissue and platysma to reach carotid sheath and passes btw carotids and opens into tonsillar sinus

Question 33

When does the thyroid take on definitive shape?

Answer 33

7 weeks and the thyroglossal duct will degenerate