Embryology 4 - The Oropharyngeal Apparatus

Question 1

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

Answer 1

Pharyngeal Arch

Question 2

What is the mesenchyme derived from in teh third week?

Answer 2

Mesoderm

Question 3

During the fourth week, most of the mesenchyme is derived from _______ cells that migrate into the ________

Answer 3

Neural crest cells; pharyngeal arches

Question 4

When the neural crest cells migrate into the arches, what does their differentiation into mesenchyme produce?

Answer 4

Maxillary and mandibular prominences

Question 5

Components of a pharyngeal arch?

Answer 5

• Artery
• Cartilaginous rod
• Muscular component
• Sensory and motor nerves

Question 6

Where does a pharyngeal arch artery arise from?

Answer 6

Truncus arteriosus from primordial heart

Question 7

What does the pharyngeal arch cartilaginous rod form?

Answer 7

The skeleton of the arch

Question 8

What does the muscular component of the pharyngeal arch differentiate into?

Answer 8

Muscles of the head and neck

Question 9

Where are the sensory and motor nerves of the pharyngeal arches derived from?

Answer 9

Neuroectoderm of the primordial brain

Question 10

The pharyngeal arches are the main formative elements of what structures?

Answer 10

• face
• nasal cavities
• mouth
• pharynx
• larynx
• neck

Question 11

During the fifth week, what happens to the second pharyngeal arch? What is produced?

Answer 11

• Second pharyngeal arch enlarges and overgrows the third and fourth
• Forms the cervical sinus

Question 12

What happens by the end of the seventh week?

Answer 12

Second and fourth arches disappear - gives head and neck smooth contour

Question 13

What does the primordial pharynx join when it widens cranially and caudally?

Answer 13

• Cranially = stomodeum
• Caudally = esophagus

Question 14

The pharyngeal endoderm lines the internal aspects of the pharyngeal arches and passes into the diverticula = ________

Answer 14

Pharyngeal pouches

Question 15

How many pairs of pharyngeal pouches are there?

Answer 15

4 (the 5th is rudimentary or absent)

Question 16

What separates the pharyngeal pouches from the pharyngeal grooves? How many layers?

Answer 16

Pharyngeal membrane = 2 layers (no mesoderm)

Question 17

Where are the pharyngeal grooves located?

Answer 17

On the outside of the embryo

Question 18

The first pharyngeal arch separates into what two prominences?

Answer 18

Maxillary and mandibular

Question 19

What does the maxillary prominence give rise to?

Answer 19

Maxilla, zygomatic bone, part of vomer

Question 20

What does the mandibular prominence give rise to?

Answer 20

Mandible (and also forms the temporal bone)

Question 21

What do the second and third pharyngeal arches form?

Answer 21

The hyoid bone

Question 22

The first and second pharyngeal cartilages give rise to what?

Answer 22

Ossicles of middle ear and styloid process of temp bone

Question 23

The fourth and sixth pharyngeal arches give rise to what?

Answer 23

Laryngeal cartilage

Question 24

The third and fourth pharyngeal arches give rise to what?

Answer 24

The epiglottis

Question 25

Which pharyngeal arch is rudimentary and eventually disappears?

Answer 25

5th

Question 26

Muscles from first pharyngeal arch?

Answer 26

• Muscles of mastication
• Muscles of middle ear

Question 27

Muscles from second pharyngeal arch?

Answer 27

• Stapedius
• Stylohyoid
• Posterior belly of digastric
• Auricular
• Muscles of facial expression

Question 28

Muscles from third pharyngeal arch?

Answer 28

• Stylopharyngeus

Question 29

Muscles from fourth pharyngeal arch?

Answer 29

• Cricothyroid
• Levator veli palatini
• Constrictors of pharynx

Question 30

Muscles from sixth pharyngeal arch?

Answer 30

• Intrinsic muscles of the larynx

Question 31

First arch nerve?

Answer 31

Trigeminal nerve (not V1)

Question 32

Second arch nerve?

Answer 32

Facial nerve

Question 33

Third arch nerve?

Answer 33

Glossopharyngeal nerve

Question 34

Fourth arch nerve?

Answer 34

Superior laryngeal (vagus nerve)

Question 35

Sixth arch nerve?

Answer 35

Recurrent laryngeal (vagus nerve)

Question 36

What does the first pharyngeal pouch expand into?

Answer 36

Tubotympanic recess (responsible for hearing)

Question 37

When the tubotympanic recess contacts the first pharyngeal groove, what forms?

Answer 37

Tympanic membrane (eardrum)

Question 38

What does the cavity of the tubotympanic recess become?

Answer 38

Tympanic cavity and mastoid antrum

Question 39

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

Answer 39

pharyngotympanic tube (eustachian tube)

Question 40

What does the second pharyngeal pouch eventually give rise to?

Answer 40

Palatine tonsils

Question 41

What does the third pharyngeal pouch develop into?

Answer 41

• Inferior part of parathyroid glands (dorsal part)
• A thymus (ventral part)

Question 42

What does the fourth pharyngeal pouch develop into?

Answer 42

Superior part of the parathyroid gland

Question 43

First endocrine gland to develop in the embryo?

Answer 43

Thyroid gland

Question 44

When does the thyroid gland begin to form? From what?

Answer 44

24 days post-fertilization from thickening in floor of primordial pharynx

Question 45

For a short tie, what is the thyroid gland connected to the tongue by?

Answer 45

Thyroglossal duct

Question 46

When is the thyroid gland usually located at its final site in the neck?

Answer 46

By week 7