Embryology III

Question 1

Face formation occurs during week

Answer 1

4

Question 2

face formation step 1

Answer 2

žFace begins as five facial primordia around stomodeum

—Frontonasal prominence (FNP)

—Paired maxillary prominences (MxP)

—Paired mandibular prominences (MdP)

Question 3

face formation step 2

Answer 3

žNasal placodes (ectodermal thickening) form on FNP

Question 4

Face formation step 3

Answer 4

žUnderlying mesenchyme around nasal placodes proliferate, creating elevations around the placodes

• —Nasal placodes “sink in” & become nasal pits, then dilate to become nasal sacs
• —Elevated regions around the nasal pit are called nasal prominences -> divided into medial and lateral portions

Question 5

face formation step 4

Answer 5

žMxPs grow & enlarge, “pushing” nasal prominences toward midline of the face

Question 6

face formation step 5

Answer 6

žMedial nasal prominences fuse (Week 6-10), giving rise to

• —Bridge of the nose
• —Intermaxillary segment
  
  • Portion of the upper lip (philtrum)
  • Upper jaw with 4 incisors
  • Primary palate

Question 7

face formation step 6

Answer 7

žMxPs fuse with the intermaxillary segment

• —Ventral region -> smooth upper lip
• —Dorsal region -> fusion of primary and secondary palate

ž

Question 8

face formation step 7

Answer 8

žLateral nasal prominences give rise to the alae of the nose

žLateral nasal prominences fuse with MxP

žAt the site of fusion, ectoderm thickens into a cord then “sinks” into underlying mesenchyme which canalizes to become the nasolacrimal duct

Question 9

face formation summary

Answer 9

1. 5 facial primordia around stomoduem
2. nasal placodes form on FNP
3. žUnderlying mesenchyme around nasal placodes proliferate, creating elevations around the placodes
4. MxPs grow & enlarge
5. Medial nasal prominences fuse (Week 6-10), giving rise to

• —Bridge of the nose
• —Intermaxillary segment

6. žMxPs fuse with the intermaxillary segment
7. nasolacrimal duct forms

Question 10

ž4 types of papillae (~week8)

Answer 10

—Filiform

—Fungiform*

—Folliate*

—Circumvallate*

*contains taste buds

Question 11

nasal cavity step 1

Answer 11

žTwo nasal pits -> nasal sacs

Question 12

nasal cavity step 2

Answer 12

žNasal sacs fuse in the midline, forming a single nasal cavity separated from oral cavity by a thin oronasal membrane

Question 13

nasal cavity step 3

Answer 13

žOronasal membrane ruptures dorsal to primary palate à oral and nasal cavity becomes continuous

Question 14

nasal cavity step 4

Answer 14

žFormation of secondary palate separates nasal cavity from oral cavity

Question 15

nasal cavity step 5

Answer 15

žNasal septum separates right and left nasal cavities

Question 16

nasal cavity step 6

Answer 16

žNasal conchae develop from the lateral walls of the nasal cavities

Question 17

nasal cavity step 7

Answer 17

žCranial ectoderm in the nasal cavity differentiate and specialize à Olfactory epithelium

Question 18

primary palate derives from ____ and gives rise to ____.

Answer 18

intermaxillary segment (fused medial nasal prominences)

anterior, triangular portion of the hard palate

Question 19

secondary palate derives from ____, gives rise to ____.

Answer 19

the fusion of palatine shelves that grow from the MxPs

the majority of hard palate and all of soft palate