Prenatal Craniofacial Development Flashcards
Dr. Timothy Cox
Neural crest cells start to form around:
3-4 weeks
Morphogenesis of the face is a complex process involving (4):
- Patterning
- Outgrowth
- Fusion
- Moulding of tissues
At around 22 days (about the end of the third week), head and neck regions comprise:
Around half of the embryo
During the fourth week of development, ventral mesoderm condenses into:
A series of segmented, bilaterally paired, mesenchymal swellings
During the fourth week of development, ________ condenses into a series of segmented, bilaterally paired, mesenchymal swellings
Ventral mesoderm
Pharyngeal/branchial arches form on the ______ side of the _____
Ventral side; neural tube
Ultimately ____ pairs of pharyngeal (branchial) arches arise in _______ order
5 pairs; cranial-caudal (anterior-posterior)
Initially _____ prominences (tissue masses) surround the stomodeum
5 prominences
List the early facial prominences:
-Frontonasal prominence
-First arch (mandibular process)
-Maxillary process (delayed appearance)
The ______ and ______ are both paired structures that grow ventro-laterally around the oropharyngeal membrane
First (mandibular) arch & maxillary process
Tucked at the back of the mouth, sort of the pivot point for embryo folding:
Oropharyngeal membrane (OM)
What happens to the oropharyngeal membrane around the fourth week of development?
It breaks down
Throughout vertebrates we see the conservation of facial morphogenesis, give examples of some structures that are conserved:
- Forming nostrils
- Mouth & oropharynx region
- Frontonasal, maxillary & mandibular processes
The majority of the growth and morphological change in facial tissue masses is driven by:
The invading cranial neural crest-derived mesenchyme
As the neural tube closes these CNCC are:
Leaving & streaming down the ventral part of the embryo
The pharyngeal arches are composed of a couple of different cell types, including:
-ectoderm (outside)
-endoderm (inside)
-mesoderm (in between)
On the inside of the pharyngeal arch we see _____ while on the outside we see _____
Pharyngeal pouches, pharyngeal clefts
The pharyngeal pouches located on the inside of the pharyngeal arches will give rise to different structures including:
-larynx
-pharynx
-other epithelial-derived structures
From days 9-10 we can see the ______ cells are really driven into the facial structures
Neural crest cells
The first paired pharyngeal arches only give rise to:
The mandibular processes
If the first paired pharyngeal arches only give rise to the mandibular processes, where do the maxillary processes originate from?
Maxillary processes originate as separate (delayed) swellings ROSTRAL to the mandibular processes
Describe the cells that give rise to the maxillary processes:
A distinct population of late migrating CNCC
The thickening of structures on the lateral aspect of the frontonasal process that will invaginate to form the nostrils:
Nasal placodes
The thickening of structures on the lateral aspect of the embryo which will eventually form the inner ear structure:
Otic placodes
Thickening of ectoderm:
Placodes
The induction and invagination of nasal placodes is similar to:
Induction and invagination of the neural plate
Placodes are extremely important because they form:
Very distinct invaginations
What are the two types of morphological processes for joining tissues of the midface?
- Merging
- Fusion
The morphological process of tissue joining that is characterized by the joining of two masses that are already partly in contact:
Merging
What process of morphological joining of tissues is responsible for the joining of the maxillary process and lateral nasal processes?
Merging
What process of morphological joining of tissues is responsible for the medial joining of the mandibular processes?
Merging
In humans, when does the merging of the lateral nasal process with the maxillary process occur?
5th week of development
The morphological process of tissue joining that is characterized by the joining of two separate tissue masses:
Fusion
What process of morphological joining of tissues is responsible for the joining of the medial nasal process and the maxillary/lateral nasal process?
Contact-dependent fusion
Contact-dependent fusion between the medial nasal process and lateral nasal process is responsible for forming:
The primary palate & nares (nostrils)
The secondary palate forms around the tenth week of development through a _____ event
Fusion
After immigration of cranial neural crest cells, growth & morphogenesis of the face is controlled by ongoing:
Epithelial-mesenchymal interactions
Responsible for determining facial form/shape:
Cranial neural crest cells
In addition to CNCCs primarily determining facial form/shape, ______ also play a role
Ectoderm
How does the ectoderm play a role in determining facial form/shape?
Defines boundaries of gene expression
What are two examples of neural expression signals provided by the ectoderm for role in facial form/shape?
Shh & FGf8
Juxta-positioned FGf8/Shh leads to:
Frontonasal ectoderm zone (FEZ)
The growth factor secreted by the ventral facial ectoderm:
Shh
The growth factor secreted by the dorsal facial ectoderm:
Fgf8
Ectodermal factors instruct:
Facial D-V patterning
Secreted factors from the FEZ can direct outgrowth of the underlying CNCC and determines:
D-V pattern of the frontonasal process (FNP)
The precise shape of the frontonasal process (FNP) depends upon pattern information inherent in the:
Neural crest
List three other functions of the ectoderm (in addition to gene expression/patterning signals):
- Support & direct outgrowth of facial processes
- Guides differentiation of CNC through growth factors
- Facilitates fusion of facial processes
Fusion between what three components of the embryo must occur in order to form the primary palate:
- Medial nasal tissue of the frontonasal process
- Lateral nasal process
- Maxillary process
For the medial nasal tissue, lateral nasal process & maxillary process to fuse to form the primary palate, what is the key player to this process?
Ectodermal cells
Fusion establishes the primary palate, which goes on to form the:
Alveolus & lip proper
How do we know that fusion of the medial nasal tissue of the frontonasal process, the lateral nasal process & the fusion are important?
Because defects in this fusion result in cleft lip or palate
Full palatal fusion is required to ensure the ______ is continuous
Alveolar bone
Third most common birth defect & occurs around 1 in 700 births world-wide
Cleft lip +/- cleft primary palate
Forms through a similar fusion mechansim as the primary palate:
Secondary palate
When does the primary palate form?
When does the secondary palate form?
7th week
10th week
Condensations of CNCC mesenchyme are:
Palatal shelves
Secondary palate formation involves: (3)
- Growth of maxillary extensions on either side of the tongue
- Elevation & rotation
- Medial growth & fusion at midline with nasal septum
________ of the secondary palate begins just before palatal development is complete
Ossification
Palatal shelves are condensations of:
CNCC mesenchyme
What is required in order to have complete mesenchyme over the bridge to form the bony part in the formation of a secondary palate?
Movement & disintigration of epithelia
Defects in palatal shelf fusion would result in a:
Cleft secondary palate
Cleft primary palate/lip occurs in ~
Cleft secondary palate occurs in~
1 in 700 births worldwide
1 in 1000 births worldwide
Cleft secondary palate can result from:
- Poor growth of shelves
- Failed elevation
- Failed fusion
What is critical for the tongue & secondary palate closure?
Critical that the tongue lowers to allow the shelves to rotate to a position above the tongue
Macroglossia (enlarged tongue) can provide a physical barrier to:
Secondary palate closure
________ is also associated with failed palatal fusion such as in Pierre-Robin Sequence
Small or retrognathic mandible
A small or retrognathic mandible results in the tongue being:
Forced backward & elevated
Craniofacial cartilage first appears in the _____ and shortly thereafter in the _____ & _____
Mandible; midface & cranial base
Provides structural support for shaping the growing head:
Craniofacial cartilage
Unlike the axial skeleton, craniofacial cartilage:
Is not typically replaced by bone
Cartilage of pharyngeal arch 1:
Meckel’s cartilage
When Meckel’s cartilage arise & what does it form?
During the 7th week of human development; template for the mandible
Pharyngeal arch 1 also contributes to two:
Ear ossicles (parts of malleus & incus)
If a patient has a mandibular defect, what also should you check for?
Inner ear deficiencies
Portion of the ear:
-Derivatives of PA1 & PA2
-Intervening pharyngeal cleft
-Pharyngeal pouch
External & middle ear
Portion of the ear:
Arises from the thickening of ectoderm (otic placode) dorsal to PA3 at the level of the hindbrain & subsequent invagination (otic pit)
Inner ear
During the development of the ear, region between PA1 & PA2 undergo a morphological change to create bulge-like structures called:
Hillocks of His
Inner & outer ear malformations are often associated with:
Mandibular defects
Ossification of the mandible & maxilla start occurring around day _____ of development
52
The cranial neural crest cells give rise to the bony structures of the _____ & _____, but NOT to the ______, as those are derived from a mesoderm component
Face & frontal bone; NOT parietal bone
