Embryology of Face, Mouth and Palate

Question 1

What is the stomodeum?

Answer 1

primitive mouth

Question 2

What are prominences?

Answer 2

5 neural crest populations around the stomodeum

Question 3

Name the 5 facial primordial prominences?

Answer 3

Single frontal nasal prominence
Paired maxillary prominences
Paired mandibular prominences

Question 4

What does the dingle frontonasal prominence form?

Answer 4

the forehead & most of nose, optic vesicles > eyes
- derived from mesenchymal cells from forebrain & midbrain neural crest cells

Question 5

What does the maxillary prominence form?

Answer 5

upper cheek regions & upper lip
- from neural crest-derived mesenchyme (1st pair of pharyngeal arches)

Question 6

What does the mandibular prominences form?

Answer 6

chin, lower lip, lower cheek
- from neural crest-derived mesenchyme (1st pair of pharyngeal arches)

Question 7

Early cranial mesoderm consists mainly of?

Answer 7

1. paraxial mesoderm
2. prechordal mesoderm
3. lateral mesoderm

Question 8

Paraxial mesoderm forms?

Answer 8

connective tissues, muscles & skeletal elements of cranial region

Question 9

Prechordal mesoderm form?

Answer 9

contributes to extraocular muscles
- located in the midline, rostral to the tip of notochord

Question 10

Lateral mesoderm forms?

Answer 10

Contributes to endothelial and smooth muscle cells

Question 11

When do the nasal cavities begin to develop?

Answer 11

End of 4th week

Question 12

What are nasal placodes?

Answer 12

thickenings of surface ectoderm
- primordia of nasal pits & nasal epithelium

Question 13

What are the nasal pits?

Answer 13

Primordial of nostrils and nasal cavities
- proliferation of mesenchyme in maxillary prominence causes them to grow towards each other

Question 14

What separates the maxillary processes and Lateral nasal prominences?

Answer 14

Nasolacrimal groove
> Epithelial cord canalizes in nasolacrimal groove to form nasolacrimal duct - carries tears from lacrimal sac to nasal

Question 15

Describe nasal placodes and how they become nasal pits?

Answer 15

thickenings of surface ectoderm nasal pits > deepening > nasal sacs

Question 16

What are oronasal membranes and what happens to them?

Answer 16

Oronasal membrane separates the oral cavity from the nasal sacs
> Membrane ruptures (end of 6th wk)
- primordial chonae (opening betwn nasal cavity and nasopharynx)

Question 17

Describe the development of the olfactory system?

Answer 17

• Ectodermal epithelium in the roof of each nasal cavity > specialized > olfactory epithelium
• Some epithelial cells differentiate into olfactory receptor cells (neurons) whose axons become olfactory nerves and grow into olfactory bulbs of the brain

Question 18

Describe the development of paranasal sinuses?

Answer 18

• From outgrowths of nasal cavity walls > pneumatic (air-filled) extensions of the nasal cavities in adjacent bones
• Original openings of the outgrowths persist as the orifices of the adult sinuses
  1. Frontal sinuses
  2. Sphenoidal or maxillary sinuses
  3. Ethmoidal sinuses
  Note: Paranasal sinuses develop in late fetal life & after birth

Question 19

Describe the development of the face at the end of the 5th week?

Answer 19

primordia of auricles (external part of ears) have begun to develop
> Six auricular hillocks (3 mesenchymal swellings on each side) form around 1st pharyngeal pouch
- auricle, external acoustic meatus
Note: initially the external ears are located in the neck region, but as the mandible develops they are located on the side of the head

Question 20

Describe the development of the face between the 7th and 10th week?

Answer 20

Medial nasal prominences merge with each other and with maxillary & lateral nasal prominences to give:
1. Middle part (philtrum) of the upper lip
2. premaxillary part of maxilla & gingiva (gum)
3. primary palate

Question 21

The first pharyngeal arch develops into?

Answer 21

Muscles of mastication (V)

Question 22

The second pharyngeal arch develops into?

Answer 22

Muscles of facial expression (VII)

Question 23

What is the labiogingival lamina?

Answer 23

thickening of ectoderm
> lips, gum, lingual frenulum

Question 24

Describe how the face changes during its development?

Answer 24

1. Early fetal period: Flat nose and underdeveloped mandible
2. Enlarging brain: Prominent forehead, medial movement of eyes & external ears rise

Question 25

When does palatogenesis take place?

Answer 25

6th - 12th week

Question 26

Describe the development of the primary palate?

Answer 26

• Median palatine process begins to develop from deep intermaxillary segment of maxilla
  -Primary palate forms the premaxillary part of the maxilla
• Represents only a small part of adult hard palate (anterior to the incisive foramen that lodges the incisor teeth)

Question 27

Describe the development of the secondary palate?

Answer 27

• Bone develops in primary palate forming the premaxillary part of the maxilla which lodges between the incisor teeth
• Bone extends from the maxillae and palatine bones into palatine processes to form the hard palate
• Posterior aspects do not ossify
• Extend posteriorly to form soft palate & uvula
• Palatine raphe permanently indicates the line of fusion of the lateral palatine processes
• Small nasopalatine canal persists
  between premaxilla and palatine
  processes as incisive fossa (opening for
  incisive canal)

Question 28

Describe palate anomalies?

Answer 28

Cleft palate - associated with cleft lip
> failure of mesenchymal masses in the lateral processes to fuse
- neural crest cells implicated
1. Anterior cleft anomalies
2. Posterior cleft anomalies
3. Unilateral clefts
4. Bilateral clefts