Embryology of the face and nose

Question 1

when does the development of the face begin?

Answer 1

At the 4th - 5th week which is when the pharyngeal arches appear, mainly develops from the 1st and 2nd arches.

Question 2

What are the pharyngeal arches?

Answer 2

Bars of mesenchyme tissue covered by surface ectoderm and inside epithelium form endoderm
- mesenchyme tissue is derived form the paraxial and lateral plate of mesoderm, neural crest cells
- neural crest cells migrate to the facial region and forms the full viscerocranium

Question 3

What form the center of the face by the end of the 4th week

Answer 3

the stomodeum with first pharyngeal arches pair
- is the depression if ectoderm for formation of the mouth

Question 4

Mesenchymal prominences (42 days)

Answer 4

2 mandibular (1 arch)
2 maxillary ( dorsal part of 1st arch)
1 frontonasal with 2 nasal prominences (thickening of surface ectoderm)

Question 5

Nerves associated to the arches

Answer 5

1 - mandibular branch of V5
2 - facial
3 - glossopharyngeal
4- superior laryngeal of vagus
6 - recurrent laryngeal of vagus

Question 6

1st pharyngeal arch structure and product

Answer 6

• Ventrally the mandibular prominences and dorsally the maxillary
• middle ear ossicles; incus and malleus from the Meckel cartilage (when it disappears)
• external ear and auditory meatus

Mesenchyme cells of the maxillary prom; maxilla, zygomatic bone and part of the temporal bone
Mesenchyme surrounding the Meckel cartilage ; mandible
–> both will form by membranous ossification

Muscles of mastication + the dermis (sensory by V5)

Question 7

2nd arch structure + product (hyoid arch)

Answer 7

Reichert cartilage ;
Stapes, styloid process of the temporal bone, stylohyoid ligament + part of the hyoid bone
Muscles of the hyoid arch

Question 8

Nasal placodes at week 5

Answer 8

invagination to nasal pit with ridges –> lateral and medial nasal prominences

Question 9

How does the upper lip form? What else is formed by the maxillary prom?

Answer 9

1. Maxillary prom. enlarge medially compressing the medial nasal prom. –> both fuse and form the upper lip
2. Enlargements of the maxillary prom –> cheeks and maxilla

Question 10

what do the mandibular prom. forms

Answer 10

They merge at the midline and form the lower lip and jaw

Question 11

Formation of the nasolacrimal duct

Answer 11

By the nasolacrimal groove (deep furrow)

Question 12

Development of the palate

Answer 12

Inter-maxillary segment –> from the medial nasal prom.
- labial component; philtrum of the upper lip
- upper jaw; 4 incisors
- palatal; CT of primary palate

Secondary palate
- palatine shelves (maxillary prominence) –> extend into the oral cavity
- in the 7th week, the shelves are horizontally positioned as the nasal septum prolongs –> the shelves fuse forming the secondary palate, soft palate and the uvula
- incisive foramen is the landmark between the two palates
By the 10th week - fusion of the secondary palate with the nasal septum

Question 13

Nasal cavities

Answer 13

Frontal prominence –> bridge of nose forehead
Medial prominence merge = crest and tip
Lateral prominence = ala of nose

• In the 6th week the nasal pits begin to deepen
• oronasal membrane (mesenchyme) that separates the nasal pits from the primitive oral cavity
  –> membrane breaks down
  7th week
  –> primitive choanae foramen on each side of the membrane
  (connection of the primitive nasal cavity open to the oral cavity)
  9 week
  definitive nasal cavity separated form the oral cavity by the 1 and 2 palate.
  –> definitive choanae lies at the junction of the nasal cavity and the pharynx