CFD 6 - face, jaws and mouth 1 Flashcards
What is the fronto-nasal process?
prominence in the upper facial area at the most cephalic end of the embryo
What is the ‘cephalic end’?
head of a structure such as the trilaminar embryonic disc
What are the mandibular processes?
processes of first branchial arch that fuse at the midline to form mandibular arch
What is the mandibular arch?
lower dental arch with mandibular teeth or the 1st branchial/pharyngeal arch inferior to the stomodeum in the embryo
What are the maxillary processes?
prominence from mandibular arch that grows superiorly and anteriorly on each side of the stomodeum of the embryo
What is the maxillary arch?
upper dental arch in which the maxillary teeth form
What is the nasal placode?
placodes that develop into olfactory organ for the sensation of smell located in the mature nose
What is a placode?
area of ectoderm found in the location of the developing special sense organs on the embryo
When during development is the basic morphology of the face established?
between the 4th and 10th week
What develops to establish the basic morphology of the face?
the 5 prominences (develop and join together)
What are the 5 prominences in face development?
- frontonasal prominence (overlies the forebrain)
- 2 maxillary prominences
- 2 mandibular prominences (associated with the 1st pharyngeal arch)
What does the frontonasal prominence arise from?
neural crest cells derived from the mid- and fore-brain
Where are the neural crest cell contributions to the maxillary and mandibular prominences derived from?
the mid- and hind-brain
What embryonic layers are involved in facial development?
all 3 (endoderm, ectoderm, mesoderm)
What should be happening to the oropharyngeal membrane during the 5th week of development?
should see disintegrating oropharyngeal membrane and these prominences growing across
What do the 5 prominences surround?
the stomodeum
What is the stomodeum?
primitive oral cavity
What separates the stomodeum from the GI tract?
an oropharyngeal membrane
What are the 2 types of fusion?
- “fusion” e.g. between medial nasal prominences
- true fusion e.g. between medial nasal prominence and maxillary process
What happens during “fusion”?
- “fusion” of prominences by elimaintion of furrow
- proliferation of cells, pushing up of surrounding tissue causing the groove to become more progressively smoother or shallow until it completely smooths out
- this merging is critical as without it, a deep depression or facial cleft would remain between what used to be the facial processes
What is true fusion?
- true fusion of separate processes
- two separate processes growing towards each other, touching, and then fusing
What is the primary palate?
- from the fused medial nasal prominences (intermaxillary segment)
- does not separate oral and nasal cavities - demarcates
What is happening at 26 days of development?
- Placodes forming - rounded areas of thickened ectoderm which will develop into special sense organs
- Maxillary processes start growing towards eachother
- Mandibular process undergoing “fusion” - groove becoming more shallow
What is happening at 27 days of development?
- Nasal pits starting to migrate in
- Maxillary processes starting to enlarge and grow across
- Mandibular process groove starting to flatten out
What is happening during day 34 of development?
- Growth of the maxillary processes also pulls round the otic placodes which will develop into the eyes
- Differentiation into medial and lateral nasal prominences
What is happening during day 36 of development?
- Pattern formation
- Thickenings now starting to differentiate on either side of the foetus
- These simultaneously start to signal and enlarge
What is happening during the 6th week of development?
the ectoderm at the centre of each of the nasal placodes invaginates to form an oval nasal pit
What do the oval nasal pits divide?
the frontonasal prominence into the lateral and medial nasal processes
What does the groove between the lateral nasal prominence and the adjacent maxillary prominence form?
the naso-lacrimal groove, or the nasal optic furrow
What happens to the medial nasal prominences by the end of the 6th week of development?
By end of 6th week the medial nasal prominence approximates towards the midline and will then join to form the primordial and the bridge in the septum of the nose
What happens to the ectoderm at the floor of the naso-lacrimal groove during the 7th week of development?
- during the 7th week the ectoderm at the floor of this groove invaginates into the underlying mesenchyme to form tubular structures called the naso-lacrimal ducts and sacs
- the nasal-lacrimal duct is invested in bone during ossification of the maxilla and after birth it functions to drain excess tears from the eye into the nasal cavity
What should we have by the end of 6 weeks of development?
formation of a basic nose structure but still got a gap between the medial nasal prominence and the maxillary arch
What should happen by the end of week 7 of development?
- the inferior tips of the medial nasal process expand laterally and inferiorly to join the intermaxillary process, to form the intermaxillary segment
- this gives rise to true fusion
- the intermaxillary process gives rise to the philtrum and then later the primary palate, and it will contain 4 incisor teeth
When should the developing face be fairly recognisable as a normal human face?
by week 10
When is the inter mandibular depression filled, and what by?
during week 4 and 5 by proliferating mesenchymal cells
When does the oropharyngeal membrane rupture to form a broad slit of the embryonic mouth?
during week 5
When is the mouth reduced to its final width?
weeks 7 and 8, as fusion of the lateral portions of the maxillary and mandibular swellings creates the cheeks
What is caused if there is too little fusion when the mouth is being reduced to its final size?
macrostomia/large mouth
What is caused if there is too much fusion when the mouth is being reduced to its final size?
microstomia/small mouth
What happens for the mouth to be reduced to its final size?
fusion of the lateral portions of the maxillary and mandibular swellings creates the cheeks
What part/s of the face does the frontonasal prominence contribute to?
forehead, bridge of nose
What part/s of the face does the medial nasal prominence contribute to?
philtrum of the lip, crest and tip of nose
What part/s of the face does the lateral nasal prominence contribute to?
alae of nose
What part/s of the face does the maxillary prominence contribute to?
cheeks, lateral upper lip
What part/s of the face does the mandibular prominence contribute to?
lower lip
What do the streams of mesenchyme into the developing face during week 6 of development do?
push back and make sure proliferation goes on, and will form areas such as the secondary palate, septum of the nose etc as they migrate in
When during development will we see the first signs of tooth development?
week 6
What is the first sign of tooth development?
primary thickenings of epithelial band, this is where the tooth will start to develop
When during development do the palatal shelves start to grow, nasal septum starts to grow down, and tongue is growing?
week 7
When during development is the oro-nasal cavity being filled up with lots of tissue, the secondary palatal shelves starting to grow down, and the nasal septum starting to migrating and push downwards?
as week 7 progresses
During week 7, what happens to the mesenchyme of the developing face?
- starting to get condensation of this mesenchyme and differentiation of it - starts to form cartilage
- mesenchymal cells differentiating into chondroblasts and start to have chondrogenic potential
- cartilage of nose being formed
What will the cartilage formed during week 7 be the primary support for?
the developing maxilla and will form the cartilages of the cranial base
During developing, when does ossification of the mandible occur?
6-7th week
During developing, when does ossification of the maxilla occur?
8th week
During developing, when does ossification of the palate and nasal capsule occur?
8th week
What are the 2 methods of osteogenesis?
- intramembranous
- endochondral
(indistinguishable in mature bone)
What is intramembranous ossification?
- the formation of an osteoid within two dense connective tissue sheets, which eventually replaces the connective tissue
- mesenchymal cells differentiate into osteoblasts from osteoid
What are the steps of intramembranous ossification?
- mesenchymal cells —> osteoblasts
- osteoblasts deposit osteoid…
- mineral deposited
- osteoblasts trapped —> osteocytes
What is endochondral ossification?
cells undergo a different lineage, start to grow round the side of the cartilage and deposit
When does the maxilla’s primary centre of intramembranous ossification (for each half of the maxilla) appear?
around week 7
Where is the maxilla’s primary centre of intramembranous ossification located?
at the termination of the infra-orbital nerve, just superior to the dental lamina of the primary maxillary canine tooth in each maxillary process
Where are secondary ossification centres for the maxilla found?
at the zygomatic, the orbital nasal, nasopalatine, and intermaxillary
- appear and fuse rapidly
What do the 2 intermaxillary ossification centres generate?
the alveolar ridge, the primary palate region
What skeletal subunits can subsequent growth of the maxilla be divided into?
- the basal body unit
- the nasal unit
- the alveolar unit
- the pneumatic unit
What does the basal body unit do?
develops under the intraorbital nerve and responds to eyeball growth
What does the nasal unit depend on?
the nasal septal cartilage
What does the alveolar unit respond to?
tooth growth in the maxilla
What does the pneumatic unit reflect?
maxillary sinus expansion
What molecules/factors have a role in the control of pattern formation?
- retinoic acid
- five growth factors families implicated in the facial development:
- BMP, FGF, Shh, Wnt and endothelins
control proliferation, survival and apoptosis
What happens if Dlx5 is knocked out?
don’t get mandible formation, maxilla is formed in both places
