Embryology of the Pharyngeal Apparatus

Question 1

During what week of development do neural crest cells migrate and form the mesenchyme of the pharyngeal arches?

Answer 1

Week 4

Question 2

What type of tissues form the pharyngeal arches?

Answer 2

mesoderm and mesenchyme

Question 3

What type of tissue forms the pharyngeal grooves?

Answer 3

ectoderm

Question 4

What type of tissue forms the pharyngeal pouches?

Answer 4

endoderm

Question 5

What is the derivative of the first pharyngeal groove?

Answer 5

external acoustic meatus (ectoderm)

Question 6

What is the derivative of the 2nd-4th pharyngeal grooves?

Answer 6

cervical sinus (endoderm) - obliterates

Question 7

What is the derivative of the first pharyngeal membrane?

Answer 7

tympanic membrane (contains all three germ layers)

Question 8

What are the mesoderm and mesenchyme derivatives of the first pharyngeal arch?

Answer 8

malleus and incus
anterior L. of malleus
sphenomandibular L.
model for the mandible
muscles of mastication

Question 9

What are the mesoderm and mesenchyme derivatives of the second pharyngeal arch?

Answer 9

stapes and styloid process
stylohyoid L.
lesser horn of hyoid bone
stapedius M.
muscles of facial expression

Question 10

What are the mesoderm and mesenchyme derivatives of the third pharyngeal arch?

Answer 10

greater horn of the hyoid bone
body of the hyoid bone
stylopharyngeus M.

Question 11

What are the mesoderm and mesenchyme derivatives of the fourth pharyngeal arch?

Answer 11

epiglottis (neural crest cells)
cricothyroid M.
levator veli palatini M.
pharyngeal constrictors

Question 12

What are the endodermal derivatives of the first pouch?

Answer 12

tympanic cavity and mastoid antrum
pharyngotympanic tube
inner surface of tympanic membrane

Question 13

What are the endodermal derivatives of the second pouch?

Answer 13

tonsils

Question 14

What are the endodermal derivatives of the third pouch?

Answer 14

inferior parathyroid glands

thymus

Question 15

What are the endodermal derivatives of the fourth pouch?

Answer 15

-superior parathyroid glands

-ultimobranchial body
fuses w/thyroid to form parafollicular cells

Question 16

When is the thymus most active?

Answer 16

childhood

Question 17

What happens to the thymus is adulthood?

Answer 17

it involutes and adipose tissue takes its place

Question 18

What gland in the body is the first to form embryologically?

Answer 18

thyroid

Question 19

Is the thyroid a pharyngeal arch derivative?

Answer 19

No

Question 20

What is the thyroid derived from?

Answer 20

an endodermal thickening and invagination of the floor of the primordial pharynx

Question 21

To what is the thyroid connected during development and how is it connected?

Answer 21

connected to tongue at the foramen cecum by thyroglossal duct

-foramen cecum closes and thryglossal duct disappears

Question 22

What are the mesoderm and mesenchyme derivatives of the sixth pharyngeal arch?

Answer 22

intrinsic laryngeal muscles

Question 23

What are cervical cysts?

Answer 23

• slowly enlarging, painless, free-lying cysts in the neck
• inferior to angle of the mandible
• remnant of cervical sinus and/or 2nd cleft/groove
• accumulation of fluid and cell debris derived from desquamation of epithelial lining

Question 24

What is a cervical sinus?

Answer 24

• failure of the 2nd pharyngeal groove and sinus to obliterate
• detected due to mucus discharge
• typically bilateral and commonly associated w/auricular sinuses

Question 25

What is a cervical fistula?

Answer 25

• abnormal canal that opens into the tonsillar sinus and externally in the side of the neck
• persistence of parts of the 2nd groove and pouch

Question 26

What is the clinical presentation of Treacher-Collins Syndrome?

Answer 26

-downward-slanted eyes, defects of lower eyelids, deformed external ears

Question 27

What is the genetic inheritance pattern of Treacher-Collins?

Answer 27

autosomal dominant

Question 28

What is the affected gene in Treacher-Collins Syndrome, what is the mutation and what does the gene normally do?

Answer 28

the TCOF1 gene is truncated, which encodes the TREACLE protein that is involved in ribosome biogenesis

Question 29

What biochemical process causes the physical deformities associated with Treacher-Collins Syndrome?

Answer 29

increased apoptosis of neural crest cells

Question 30

What is the clinical presentation of Pierre-Robin Sequence?

Answer 30

• hypoplasia of mandible
• bilateral cleft palate
• defects in eyes and ears
• micrognathia, which leads to posterior displacement of tongue

Question 31

In thyroid agenesis, specifically hemiagenesis, which lobe is more commonly missing?

Answer 31

left

Question 32

In thyroid hemiagenesis, mutations in what receptor are also likely involved?

Answer 32

receptors for TSH

Question 33

What is the clinical presentation of DiGeorge Syndrome?

Answer 33

congenital hypoparathyroidism
shortened philtrum of upper lip
low-set, notched ears
nasal clefts
thyroid hypoplasia
cardiac abnormalities (defects of heart and aortic arch)

Question 34

What is the biochemical mechanism that causes DiGeorge Syndrome?

Answer 34

breakdown of signaling from pharyngeal arch endoderm to neural crest cells, which leads to agenesis of thymus and parathyroid glands