Embryology 4

Question 1

what is pharyngeal arch?

Answer 1

a core of mesenchyme covered externally by ectoderm and internally by endoderm

Question 2

what happens during the fourth week?

Answer 2

During the fourth week, most of the mesenchyme is derived from neural crest cells that migrate into the pharyngeal arches
- migration of neural crest cells into the arches and their differentiation into mesenchyme produces the maxillary and mandibular prominences

Question 3

a pharyngeal arch contains

Answer 3

○ A pharyngeal arch artery that arises from the truncus arteriosus of the primordial heart and passes around the primordial pharynx to enter the dorsal aorta
○ 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

what is the main formative elements of the face, nasal cavities, mouth, larynx, pharynx, and neck?

Answer 4

the pharyngeal arches

Question 5

During the fifth week, the second pharyngeal arch enlarges and overgrows the third and fourth arches, forming

Answer 5

cervical sinus

Question 6

when does the second to fourth pharyngeal grooves and the cervical sinus disappear
, giving the neck a smooth contour

Answer 6

by the end of the 7th week

Question 7

what widens cranially where it joins the stomodeum, and narrows caudally where it joins the esophagus

Answer 7

primordial pharynx

Question 8

the primordial pharynx is derived from what?

Answer 8

the foregut

Question 9

what is the pharyngeal pouches

Answer 9

The pharyngeal endoderm lines the internal aspects of the pharyngeal arches and passes into diverticula (outpouchings)

Question 10

how many pairs of pharyngeal pouches are there?

Answer 10

four pairs of pharyngeal pouches; the fifth pair is rudimentary or absent

Question 11

how is the pharyngeal membrane formed

Answer 11

endoderm of the pouches contacts the ectoderm of the pharyngeal grooves and together

Question 12

what does the pharyngeal membrane separate?

Answer 12

separates the pharyngeal pouches from the pharyngeal grooves

Question 13

when does the pharyngeal arches begin to develop?

Answer 13

early in the fourth week

Question 14

when the pharyngeal arches begin to develop, what cells migrate into the ventral parts of the future head and neck regions?

Answer 14

neural crest cells

Question 15

what are the first pair of pharyngeal arches turn into

Answer 15

the jaws

Question 16

the first pharyngeal arch separates into 2 prominences, what are the prominences?

Answer 16

maxillary prominence and the mandibular prominence

Question 17

what does the maxillary prominence give rise to?

Answer 17

maxilla, zygomatic bone, and a portion of the vomer

Question 18

what does the mandibular prominence forms?

Answer 18

mandible and the squamous temporal bone

Question 19

what does the second and third pharyngeal arches form?

Answer 19

the hyoid bone

Question 20

what does the first and second pharyngeal cartilages give rise to?

Answer 20

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

Question 21

what give rise to the laryngeal cartilage?

Answer 21

fourth and sixth pharyngeal arches

Question 22

what give rise to the epiglottis?

Answer 22

3rd and 4th pharyngeal arches

Question 23

what does the fifth pharyngeal arch form?

Answer 23

it is rudimentary - nothing is derived from it, and it disappears

Question 24

the first pharyngeal pouch expands into a ?

Answer 24

tubotympanic recess

Question 25

The expanded distal part of this recess contacts the first pharyngeal groove -> contributes to the formation of the ?

Answer 25

tympanic membrane (eardrum)

Question 26

the cavity of the tubotympanic recess becomes the ?

Answer 26

tympanic cavity and mastoid antrum

Question 27

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

Answer 27

pharyngotympanic tube (auditory tube, Eustachian tube)

Question 28

the second pharyngeal pouch eventually gives rise to parts of the ?

Answer 28

palatine tonsils

Question 29

by the sixth week, the third pouch develops:

Answer 29

○ Into parathyroid glands – dorsal part (inferior pair)
○ Into a thymus – ventral part

Question 30

the fourth pouch also develops into ?

Answer 30

parathyroids - the superior pair

Question 31

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

Answer 31

thyroid gland

Question 32

For a short time, the thyroid gland is connected to the tongue by a narrow tube, what is it called?

Answer 32

thyroglossal duct

Question 33

the thyroid gland begins to form 24 days after fertilization from a median endodermal thickening in the floor of the primordial pharynx, this thickening forms a small outpouching called

Answer 33

thyroid primordium