Development of the Face Flashcards
What is the first evidence of the development of the face?
The appearance of the stomadaeum
What is the stomadaeum?
A depression in the ectoderm on the ventral aspect of the head
What is the stomadauem the site of?
The future mouth
How is the stomodeum seperated from the anterior end of the foregut?
By the buccopharyngeal membrane
Describe the ectoderm, mesoderm, and endoderm arrangement at the buccopharyngeal membrane?
No mesoderm between ectoderm/endoderm
What form around the stomadauem?
Five folds (prominences/processes)
What are the prominences/processes that form around the stomadauem?
- Frontonasal prominence
- Maxillary prominences (2)
- Mandibular prominences (2)
Where does the frontonsal prominence form?
Superiorly, in the midline
What does the frontonasal prominence form?
- Forehead
- Bridge of nose
- Upper eyelids
- Centre of upper lip
Where are the maxillary prominences?
Laterally
What are the maxillary prominences derived from?
The 1st pharyngeal arch
What do the maxillary prominences form?
- Middle third of face
- Upper jaw
- Most of the lip
- Sides of the nose
Where are the mandibular prominences?
Inferolaterally
What are the mandibular prominences derived from?
The 1st pharyngeal arch
What do the mandibular prominences form?
- Lower 1/3 of the face
- Lower jaw
- Lip
What do the facial prominences consist of?
Mesenchyme with a covering of ectoderm
What will eventually happen to the facial prominences?
They will fuse together to complete the face
What results from the failure of fusion of the facial prominences?
Facial clefts and cleft lip
What is the first evidence of nose formation?
The apperance of bilateral ectodermal thickenings, the nasal placodes
Where do the nasal placodes first appear?
On the venterolateral aspect of the frontonasal prominence
What happens to the nasal placodes?
They invaginate to form the nasal pits
What is the entrance of each nasal pit?
The nostril
What forms around the entrance to each nostril?
A horse-shoe shaped ring
What are the ‘arms’ of the horseshoe around the nostril?
The medial and lateral nasal prominences
Where do the deepening nasal pits lie?
Dorsal to the stomodaeum
What seperates the nasal pits?
A thin sheet of cells, the oronasal membrane
What happens to the oronasal membrane?
It disappears, and the oral and nasal cavities become one continuous space
In what direction does the maxillary prominence grow?
Medially
What happens when the maxillary prominences grow medially?
They push the nasal prominences closer together in the midline
What do the maxillary prominences fuse with?
The medial nasal prominences
Where do the medial nasal prominences fuse?
In the midlien
What does the seperation of the oral and nasal cavity require?
The development of the palate
What does the development of the palate involve?
Both the maxillary and medial nasal prominences
What happens when the medial nasal prominences fuse in the midline?
It seperates the nostrils from the mouth
What does the seperation of the nostrils from the mouth by the fusion of the medial nasal prominences give rise to?
- Philtrum of the upper limb (groove)
- Median part of the maxillary bone, with itrs four incisor teeth
- Primary palate (or premaxillary portion)
What is the primary palate?
A small midline component of the palate
What grows from each maxillary prominence?
A palatal shelf
In what direction does the palatal shelf grow?
Towards the midline
What happens to the palatal shelves?
They fuse with each other, and with the primary palate
What creates the secondary palate?
Fusion
What does the secondary palate do?
Seperates the nasal cavity from the oral cavity
What does the mandible need to grow large enough to do?
Allow the tongue to ‘drop’ out of the way, allowing the fusion of the palatal shelves
How does the nasal septum develop?
As a midline down-growth
What ultimately happens to the nasal septum?
It fuses with the palatal shelves
What does a cleft palate result from?
Failure of one or both of the palatal shelves to reach the midline and fuse with its counterpart
What does a lateral cleft lip result from?
Failure of fusion of the medial nasal prominence and maxillary prominence
What is a cleft lip combined with in a cleft palate?
Failure of platal shelves to meet in midline
When does the development of the eyes begin?
In the 4th week
How does the development of the eyes begin?
With out-pockets of the forebrain
What happens to the out-pockets of the forebrain in development of the eyes?
They grow to make contact with the overlying ectoderm,
What does the contact between the out-pockets of the brain and the overlying ectoderm cause?
Changes in the ectoderm that form the optic placodes
What do the optic placodes become?
The lens of the eyes
What happens to the optic/lens placodes do after formation?
Invaginate and pinch off
When do eyelids begin to develop?
At the end of the embryonic period (week 8)
Describe the developmental programme of the eyelids
They are fused together during the second trimester, and reopen in the third
Where are the primordia of the eyes positioned?
On the side of the head
What happens to the eyes as the facial prominences grow?
The eyes move to the front of the face
What does the external auditory meatus develop from?
The 1st pharyngeal cleft
What do the auricles develop from?
Within and 1st and 2nd pharyngeal arch
Which auricles develop from the 1st pharyngeal arch?
- Malleus
- Incus
What develops from the 2nd pharyngeal arch?
Stapes
What are the otic placodes made from?
Ectoderm that thickens before sinking
What happens when the otic placodes invaginate?
They form the auditory vesicles
Where do the external ears intially develop?
In the neck
What happens to the ears as the mandible grows?
The ears ascend to the side of the head to lie in line with the eyes
What common chromosomal abnormalities have associated external ear abnormalities?
All
What does alcohol during pregnany cause?
Classic facial symptoms;
- Small eye/nose opening
- Thin Philtrum
- Under-developed jaw
What is the safe level of alcohol consumption during pregnancy?
No known safe level
What organs development is known to be sensitive to alcohol?
The brain
What is pathology of the brain related to alcohol during pregnancy traced back to?
Migration of neural crest cells
