Face, Palate and Nasal Cavity Embryology Flashcards
What are the bulges of mesenchymal tissue that protrude from both sides of the rostral embryo surrounding the stomodeum?
the pharyngeal arches (or branchial arches)
How many pharyngeal arches are there?
6 (although 5 disappears)
The 1st pharyngeal arch has two projections, which are…
the maxillary and mandibular prominences - they immediately surround the primitive mouth
At what point during development do the pharyngeal arches s=appear?
4th week
What cells invade the mesenchyme of the pharyngeal arches to form most of the facial features?
neural crest cells
What does the stomodeum develop into? The floor forms what membrane?
the mouth
the floor forms the oropharyngeal membrane which breaks down around day 24
What facial prominence is rostral to the maxillary and mandibular prominences?
the frontal prominence
What are placodes?
areas of thickening in the embryonic epitheliual layer
they will give rise to some structure or organ - in the face they do the sensory organs like the nose (nasal placodes)
Besides the nasal placodes, what are the other two sets in the face?
the lens placodes and otic placodes
At first, the otic and lens placodes are located on the ___ of the head
side of the head
the lens placodes will move to the front as the head developes
THe mandibular prominence fuses at the ventral midline during week 4. What type of ossification occurs to form the mandible?
endochondral ossification
The frontonasal prominence developes the nasal placodes during the 5th week, and during the 6th week, what developes?
the nasal pits - a depression in the center of the nasal placode that will form the nostril
During week 6, the medial nasal prominences migrate towards each other and fuse in the midline to form the ___ and ____
nasal septum and intermaxillary segment
What will the intermaxillary segment give rise to?
the philtrum
pre-maxilla
primary palate
The maxillary prominences will grow medially and fuse with the naal prominences and mandibular prominences to form what?
the cheek, upper lip and secondary palate
There is a cord of endothelium that descends deep to the nasolacrimal groove at the junction of the maxillary and forntal prominences. What does this form? How?
the nasolacrimal duct and the nasolacrimal sac
It undergoes apoptosis to canalize
The palate forms between weeks 5 and 23, but what is the criticla period for palate developemtn?
from week 6 to 9
What forms the primary palate? What forms the secondary palate?
primary palate is from the intermaxillary segment
secondary palate is from the palatine shelves of the maxillary prominences
THe palatine shelves forming the secondary palate are initially oriented downward on either side of the developing tongue, but move to the horixontal due to what?
hydration of hyaluronic acid in the mesenchymal cells of the palatine shelves
What is the last part of the palate to fuse? When?
the uvula - 12 weeks
What spot marks the fusion point of the primary and secondary palates?
THe incisive foramen
What nerves and vessel travels thoruhg the incisive canal to spread across the hard palate?
the nasopalatine nerve and terminal branches of the sphenopalatine artery
What sort of ossification does the primary palate and rostral secndary palate undergo?
intramembranous
The posterior secondary palate becomes what?
the soft palate - skeletal muscle
THe nasal sepatum from the medial nasal prominences will grow down and fuse with the palate to form what?
the perpendicular plate of the ethmoid and the vomer
What causes anterior defects of the lip and palate?
failure of the maxillary prominences to fuse with the medial nasal prominences
What causes posteiror defects of the lip and palate?
failure of the palatine shelves to fuse with one another
also failure to fuse with the septum and posterior margin of the primary palate (this will involve both hard and soft palate)
SPecifically, what might cause cleft palate issues?
any teratogen that interferes with migration of neural crest cells - this means there isn’t enough mesenchym to work this
anticonvulsants like dilantin, vitamin A, isotretinoin
Also genetic causes - trisomy 13 will do it, or single gene mutations
WHat is the prevalnece of cleft lip? More in gender? Correlated with what in the mother?
1/1000 births
60-80% males
increases with increasing maternal age
What is the prevalence of cleft palate? More in one gender? Associated with anything in the mother?
1/2500 births
twice as common in girls (probably because the palatal shelves close later in girls)
no association with maternal age
THe oroanasal membrane consists of epithelium derived from what layer?
surface ectoderm
The oral epithelium separates what two areas?
the nasal pites form the primitive oral cavity
When does the oral epithelium rupture? What does this form?
about week 6
this forms the primitive choanae
What eventually forms the definitive choanae?
formation of the secondary palate
What causes choanal atresia? WHy is this an issue in newborns?
failure of the oronasal membrane to rupture - it blocks the nose basically
it’s bad bacause newborns are obligate nasal breathers and only mouthe breathe when crying
so babies with choanal atresia will be cyanotic until they start crying, which is when they pink up
What are some developmental processes that change the shape of the face?
- growth of the paranasal air sinunses (only maxillary and part of ethmoid are present at birth - rest have to grow)
- nasal conchae formation causes elevation on lateral walls
- tooth development - trophic for bone development in jaw
Why might fetal alcohol syndrome be associated with different facial features?
they think alcohol interferes with the migration of cells - neuron sin the CNS and neural crest cells in the face
What are some of the features one might see in a child with FAS?
flat midface, short nose, indistinct philtrum, thin upper lip, minor ear anomalies, micrognathia, epicanthal folds, low nasal bridge, short palpebral fissures
