Face, Palate and Nasal Cavity Embryology

Question 1

What are the bulges of mesenchymal tissue that protrude from both sides of the rostral embryo surrounding the stomodeum?

Answer 1

the pharyngeal arches (or branchial arches)

Question 2

How many pharyngeal arches are there?

Answer 2

6 (although 5 disappears)

Question 3

The 1st pharyngeal arch has two projections, which are…

Answer 3

the maxillary and mandibular prominences - they immediately surround the primitive mouth

Question 4

At what point during development do the pharyngeal arches s=appear?

Answer 4

4th week

Question 5

What cells invade the mesenchyme of the pharyngeal arches to form most of the facial features?

Answer 5

neural crest cells

Question 6

What does the stomodeum develop into? The floor forms what membrane?

Answer 6

the mouth

the floor forms the oropharyngeal membrane which breaks down around day 24

Question 7

What facial prominence is rostral to the maxillary and mandibular prominences?

Answer 7

the frontal prominence

Question 8

What are placodes?

Answer 8

areas of thickening in the embryonic epitheliual layer

they will give rise to some structure or organ - in the face they do the sensory organs like the nose (nasal placodes)

Question 9

Besides the nasal placodes, what are the other two sets in the face?

Answer 9

the lens placodes and otic placodes

Question 10

At first, the otic and lens placodes are located on the ___ of the head

Answer 10

side of the head

the lens placodes will move to the front as the head developes

Question 11

THe mandibular prominence fuses at the ventral midline during week 4. What type of ossification occurs to form the mandible?

Answer 11

endochondral ossification

Question 12

The frontonasal prominence developes the nasal placodes during the 5th week, and during the 6th week, what developes?

Answer 12

the nasal pits - a depression in the center of the nasal placode that will form the nostril

Question 13

During week 6, the medial nasal prominences migrate towards each other and fuse in the midline to form the ___ and ____

Answer 13

nasal septum and intermaxillary segment

Question 14

What will the intermaxillary segment give rise to?

Answer 14

the philtrum

pre-maxilla

primary palate

Question 15

The maxillary prominences will grow medially and fuse with the naal prominences and mandibular prominences to form what?

Answer 15

the cheek, upper lip and secondary palate

Question 16

There is a cord of endothelium that descends deep to the nasolacrimal groove at the junction of the maxillary and forntal prominences. What does this form? How?

Answer 16

the nasolacrimal duct and the nasolacrimal sac

It undergoes apoptosis to canalize

Question 17

The palate forms between weeks 5 and 23, but what is the criticla period for palate developemtn?

Answer 17

from week 6 to 9

Question 18

What forms the primary palate? What forms the secondary palate?

Answer 18

primary palate is from the intermaxillary segment

secondary palate is from the palatine shelves of the maxillary prominences

Question 19

THe palatine shelves forming the secondary palate are initially oriented downward on either side of the developing tongue, but move to the horixontal due to what?

Answer 19

hydration of hyaluronic acid in the mesenchymal cells of the palatine shelves

Question 20

What is the last part of the palate to fuse? When?

Answer 20

the uvula - 12 weeks

Question 21

What spot marks the fusion point of the primary and secondary palates?

Answer 21

THe incisive foramen

Question 22

What nerves and vessel travels thoruhg the incisive canal to spread across the hard palate?

Answer 22

the nasopalatine nerve and terminal branches of the sphenopalatine artery

Question 23

What sort of ossification does the primary palate and rostral secndary palate undergo?

Answer 23

intramembranous

Question 24

The posterior secondary palate becomes what?

Answer 24

the soft palate - skeletal muscle

Question 25

THe nasal sepatum from the medial nasal prominences will grow down and fuse with the palate to form what?

Answer 25

the perpendicular plate of the ethmoid and the vomer

Question 26

What causes anterior defects of the lip and palate?

Answer 26

failure of the maxillary prominences to fuse with the medial nasal prominences

Question 27

What causes posteiror defects of the lip and palate?

Answer 27

failure of the palatine shelves to fuse with one another

also failure to fuse with the septum and posterior margin of the primary palate (this will involve both hard and soft palate)

Question 28

SPecifically, what might cause cleft palate issues?

Answer 28

any teratogen that interferes with migration of neural crest cells - this means there isn’t enough mesenchym to work this

anticonvulsants like dilantin, vitamin A, isotretinoin

Also genetic causes - trisomy 13 will do it, or single gene mutations

Question 29

WHat is the prevalnece of cleft lip? More in gender? Correlated with what in the mother?

Answer 29

1/1000 births

60-80% males

increases with increasing maternal age

Question 30

What is the prevalence of cleft palate? More in one gender? Associated with anything in the mother?

Answer 30

1/2500 births

twice as common in girls (probably because the palatal shelves close later in girls)

no association with maternal age

Question 31

THe oroanasal membrane consists of epithelium derived from what layer?

Answer 31

surface ectoderm

Question 32

The oral epithelium separates what two areas?

Answer 32

the nasal pites form the primitive oral cavity

Question 33

When does the oral epithelium rupture? What does this form?

Answer 33

about week 6

this forms the primitive choanae

Question 34

What eventually forms the definitive choanae?

Answer 34

formation of the secondary palate

Question 35

What causes choanal atresia? WHy is this an issue in newborns?

Answer 35

failure of the oronasal membrane to rupture - it blocks the nose basically

it’s bad bacause newborns are obligate nasal breathers and only mouthe breathe when crying

so babies with choanal atresia will be cyanotic until they start crying, which is when they pink up

Question 36

What are some developmental processes that change the shape of the face?

Answer 36

• growth of the paranasal air sinunses (only maxillary and part of ethmoid are present at birth - rest have to grow)
• nasal conchae formation causes elevation on lateral walls
• tooth development - trophic for bone development in jaw

Question 37

Why might fetal alcohol syndrome be associated with different facial features?

Answer 37

they think alcohol interferes with the migration of cells - neuron sin the CNS and neural crest cells in the face

Question 38

What are some of the features one might see in a child with FAS?

Answer 38

flat midface, short nose, indistinct philtrum, thin upper lip, minor ear anomalies, micrognathia, epicanthal folds, low nasal bridge, short palpebral fissures