H&N Embryonic overview Flashcards
What is the 1st evidence of face development?
Appearance of a depression in the ectoderm
Ventral aspect of head
Known as stomadaeum (future mouth)
5 folds (prominences) form around the stomadaeum to create the face. What are they?
Frontonasal Prominence Maxillary Prominences (2) Mandibular prominences (2)
What structures does the frontonasal prominence (FNP) go on to develop?
Superiorly, in the midline:
- Forehead
- Bridge of nose
- Upper eyelids
- Centre of upper lip (philtrum)
What structures do the maxillary prominences go on to develop?
Laterally:
- Derived from 1st Ph Arch
- Middle third of face
- Upper jaw
- Most of lip
- Sides of nose
What structures do the mandibular prominences go on to develop?
Inferolaterally:
- Derived from 1st Ph Arch
- Lower third of face
- Lower jaw
- Lip
What do the prominences consist of?
Mesenchyme
Covering of ectoderm
Eventually fuse together to complete face
What is the 1st evidence of nose formation?
Bilateral ectoderm thickenings - Nasal placodes
Ventrolateral aspect of FNP
How are nasal pits (and nostrils) formed?
Nasal placodes invaginate to form nasal pits
Entrance to each pit is future nostril
Horseshoe shaped ring forms around entrance of each nostril (medial & lateral nasal prominences)
Where do the deepening nasal pits lie initially?
Dorsal to stomadaeum
Separated only by thin sheet of cells - oronasal membrane
Oronasal membrane disappears
Oral & Nasal cavities become one continuous space
How does the nose end up in the middle of the face?
Maxillary prominences grow medially, pushing Nasal prominences closer together in midline
Maxillary prominences fuse with the Medial Nasal prominences
Medial Nasal prominences fuse in midline
How are the oral & nasal cavities separated?
Palate formation
The medial nasal prominences fuse in the midline, separating the nostrils from the mouth. What other structures arise from this?
Philtrum of upper lip (groove)
Median part of the Maxillary bone & 4 incisor teeth
Primary palate (small midline component)
How is the secondary palate formed?
A palatal shelf from each maxillary prominence grows towards midline
Fuse with each other & primary palate
Secondary palate formed - separates nasal & oral cavities
What allows the palatal shelves to fuse?
Mandible grows large enough
Allows tongue to ‘drop’ out of way
How is the nasal septum formed?
Midline down-growth
Fuses with palatal shelves
What is a cleft palate?
Congenital abnormality
Failure of one or both palatal shelves to reach the midline and fuse with its counterpart
How does a lateral cleft lip occur?
Failure of fusion of medial nasal prominence and maxillary prominence
How does a cleft lip and cleft palate occur?
Failure of fusion of medial nasal prominence and maxillary prominence
Plus, failure of palatal shelves to meet in midline
How do the eyes develop?
4th week
Out-pockets of forebrain grow
Make contact with overlying ectoderm
Form optic placodes - becomes lens of eyes
Optic/Lens placodes then invaginate & pinch off
When do the eyelids develop?
Begin at end of embryonic period (week 8)
Fused together during 2nd trimester
Reopen in 3rd trimester
What is the positioning of the eyes?
Primordia of eyes positioned at side of head
Move to front of face as facial prominences grow
What does the external auditory meatus develop from?
1st Ph Cleft
What do the auricles of the ear develop from?
1st & 2nd Ph Arches
1st - Malleus, Incus
2nd - Stapes
How are the auditory vesicles formed?
Otic placodes invaginate (ectoderm, thickens before sinking)
What is the positioning of the ears?
External ears initially develop in the neck
As mandible grows, ears ascend to side of head
Lie in line with the eyes
What is foetal alcohol syndrome?
Alcohol crosses the placenta freely during pregnancy
- Small eye/nose opening
- Thin philtrum
- Under-developed jaw
No known safe level of consumption
Neural crest cells & brain development sensitive
