Embryology 4 - The Oropharyngeal Apparatus (Week 9)

Question 1

a core of mesenchyme (embryonic connective tissue) covered externally by ectoderm and internally by endoderm

Answer 1

pharyngeal arch

Note: pharyngeal arches are the main formative elements of the face, nasal cavities, mouth, larynx, pharynx, and neck

Question 2

Migration of ___________ into the arches and their differentiation into mesenchyme produces the maxillary and mandibular prominences

Answer 2

neural crest cells

Question 3

What does a pharyngeal arch contain?

Answer 3

• an artery that arises from the truncus arteriosus (aortic trunk) of the primordial heart
• a cartilaginous rod that forms the skeleton of the arch
• a muscular component that differentiates into muscles in the head and neck
• sensory and motor nerves that supply the mucosa and muscles derived from the arch (derived from neuroectoderm of the primordial brain)

Question 4

During the 5th week, the second pharyngeal arch gets bigger and overgrows the third and fourth arches, forming an ectodermal depression on the outside of the developing pharynx called what?

Answer 4

cervical sinus

Question 5

True or False: By the end of the 5th week, all of the arches disappear, creating a smoother appearance

Answer 5

False

By the end of the 7th week

Question 6

At the pharyngeal grooves, there are only two layers. What are they?

Answer 6

ectoderm and endoderm

(NO mesoderm)

Question 7

Pharyngeal grooves are on the _________ (inside/outside) of the developing pharynx and pharyngeal pouches are on the __________ (inside/outside)

Answer 7

outside,

inside

Question 8

How many pharyngeal pouches are there?

Answer 8

4

Question 9

The _____________ separates the pharyngeal pouches from the pharyngeal grooves

Answer 9

pharyngeal membrane

Recall: only has 2 layers (ectoderm and endoderm, NO mesoderm)

Question 10

When do pharyngeal arches begin to develop?

Answer 10

early in 4th week

Question 11

The first pair of pharyngeal arches = the primordium of what?

Answer 11

the jaws

Question 12

The first pharyngeal arch (mandibular arch) separates into two prominences. What are they?

Answer 12

1) maxillary prominence

2) mandibular prominence

Note: even though the first pharyngeal arch is also known as the “mandibular arch”, it doesn’t just give rise to the mandible

Question 13

gives rise to the maxilla, zygomatic bone, and a portion of the vomer

Answer 13

maxillary prominence

Question 14

gives rise to the mandible and squamous temporal bone

Answer 14

mandibular prominence

Question 15

The second and third pharyngeal arches give rise to the _________ (which bone/cartilage derivative?)

Answer 15

hyoid bone

second arch = upper part of hyoid bone, stapes, and styloid process

third arch = lower part of hyoid bone

Question 16

The fourth and sixth pharyngeal arches give rise to the ________________ (which bone/cartilage derivative?)

Answer 16

laryngeal cartilage (thyroid cartilage, cricoid cartilage)

Question 17

The third and fourth pharyngeal arches give rise to _____________ (which bone/cartilage derivative?)

Answer 17

the epiglottis

Question 18

The first and second pharyngeal arches give rise to ________________(which bone/cartilage derivative?)

Answer 18

the ossicles of the middle ear and the styloid process of the temporal bone

first arch = malleus, incus
second arch = stapes

Question 19

True or False: The fifth pharyngeal arch also gives rise to the thyroid cartilage

Answer 19

False.

The fifth pharyngeal arch is rudimentary, as nothing is derived from it and it disappears

Question 20

The first pharyngeal arch gives rise to _______________ (which muscular derivative(s)?)

Answer 20

• muscles of mastication*
• muscles of middle ear

Question 21

The second pharyngeal arch gives rise to __________________(which muscular derivative(s)?)

Answer 21

• stapedius
• stylohyoid
• posterior belly of digastric muscles
• auricular
• muscles of facial expression*

Question 22

The third pharyngeal arch gives rise to ___________________ (which muscular derivative(s)?)

Answer 22

• stylopharyngeus

Question 23

The fourth pharyngeal arch gives rise to ______________(which muscular derivative?)

Answer 23

• cricothyroid
• levator veli palatini
• constrictors of the pharynx

Question 24

The sixth pharyngeal arch gives rise to _________________(which muscular derivative(s)?)

Answer 24

• intrinsic muscles of the larynx

Question 25

True or False: The fifth pharyngeal arch has no muscle derivatives

Answer 25

True

Question 26

What are the associated cranial nerves for each of the following pharyngeal arches?

First =
Second =
Third =
Fourth & Sixth =

Answer 26

First = trigeminal nerve (except V1)

Second = facial nerve

Third = glossopharyngeal nerve

Fourth & Sixth = vagus nerve

Question 27

The first pharyngeal pouch expands into a tubotympanic recess, whereby the distal part of this recess contacts the first pharyngeal groove. This contributes to the formation of what?

Answer 27

the tympanic membrane (eardrum)

Note: this forms between the first and second arches

Question 28

The cavity of the tubotympanic recess becomes the ________________ where the bones of the middle ear are found and the _______________

Answer 28

tympanic cavity,

mastoid antrum

Question 29

The connection of the tubotympanic recess with the pharynx elongates and forms the ____________________

Answer 29

pharyngotympanic tube (aka the Eustachian tube, aka the auditory tube)

Question 30

The second pharyngeal pouch gives rise to __________

Answer 30

parts of the palatine tonsils

Question 31

The dorsal part of the third pouch develops into _____________

Answer 31

the inferior parathyroid glands

Question 32

The ventral part of the third pouch develops into _______________

Answer 32

the thymus

Note: defects with third pouch related to DiGeorge Syndrome

Question 33

The fourth pouch develops into _______________

Answer 33

the superior parathyroids

Question 34

True or False: There are no fifth or sixth pouches

Answer 34

True

Question 35

What is the first endocrine gland to develop in the embryo?

Answer 35

the thyroid gland

Note: it forms from a median endodermal thickening in the floor of the primordial pharynx beginning ~ day 24

Note: the thyroid gland does NOT develop from the pharyngeal arches but it develops at the same time and in the same area

Question 36

For a short time, the thyroid gland is connected to the tongue via what?

Answer 36

thyroglossal duct

Note: by week 7 this degenerates and the thyroid gland is located in its final site