Week 3 - Ach (Embryo of Face/Palate) Flashcards
Where do the facial prominences develop?
Rostral end of the embryo surrounding the rostral opening of the primitive gut (stomodeum).
The five facial prominences form as what cells proliferat and migrate into the pharyngeal arches?
Neural crest cells
What makes up the frontonasal prominence?
Mesenchyme ventral to the brain vesicles
What makes up the bilateral maxillary prominences?
Extensions from the first part of the first pharyngeal arch mesenchyme
What makes up the bilateral mandibular prominences?
Second part of the first pharyngeal arch mesenchyme
What structures does the frontonasal prominence give rise to?
- Forehead
- Dorsal aspect of the nose
- Lateral nasal prominences
- sides of the nose
- Medial nasal prominences
- intermaxillary segment
- midline of the nose
- nasal septum
- philtrum (midline portion of upper lip)
- upper jaw component of maxilla
- Primary Palate
What structures do the bilateral maxillary prominences give rise to?
- Medial nasal prominences
- Check/mid-region of the face
- Most of the Maxilla
- Most of the Upper Lip
- Secondary palate
- Lateral nasal prominences
- Nasolacrimal groove
- Nasolacrimal sac & duct
What structures do the bilateral mandibular prominences form?
- Lower lip
- Jaw
- Inferior part of the face
What are placodes?
Ectodermal thickenings with neurogenic potential that appear in pairs on the developing head.
***Special senses
What are the thre placodes? What do they become?
- Lens placodes –> lens of the eye
- Otic placodes –> Inner ear
- Nasal placodes –> nasal cavity and part of upper lip
What is the Stomodeum?
Depression in the ectoderm surrounded by five facial prominences.
***Future site of the mouth.
What forms the floor of the Oropharyngeal (buccopharyngeal) Membrane?
Surface ectoderm from the stomodeum
Where is the Oropharyngeal (buccopharyngeal) Membrane located?
At the junction of the anterior 2/3 and posterior 1/3 of the tongue.
When does the Oropharyngeal (buccopharyngeal) Membrane break down and open the primitive gut to the amniotic cavity?
Around day 24
When is the most critical period of development of the palate?
End of Week 6 - Beginning of Week 9
What does the primary palate develop from?
Frontonasal prominence –>
Medial nasal prominences –>
Intermaxillary segment –> PRIMARY PLATE!
The primitive primary palate becomes what in an adult?
Portion of hard palate immediately behind the upper incisor teeth and area anterior to the incisive foramen.
What does the Secondary Palate develop from?
Maxillary prominences –>
Medial nasal prominences –>
SECONDARY PALATE!
How does the Secondary Palate form/grow?
- Palatine shelves grow toward the midline from medial aspects of the maxillary prominences
- Initially orientated down below tongue
- Shelves elevate to horizontal above tongue
- Fuse in midline (anterior –> posterior)
What part of the Secondary Palate is the last to fuse at about 12 weeks?
UVULA!
What landmark mards the fusion of the Primary and Secondary Palates?
Incisive foramen
How does the bone develop in the hard palate?
(i.e. endochondral or intramembranous)
Intramembranous ossification
Instead of becoming ossified, the soft palate develops what kind of tissue?
Skeletal muscle
What factors affect facial structures as we age?
- Development and expansion of the paranasal sinuses
- Mandible and maxilla grow and change shape in conjunction with tooth development
- Growth of nasal septum and conchae enlarge the nose
How do the nasal pits form?
Nasal placodes invaginate
What forms the base of the nasal placode/pit?
olfactory epithelium
What does the base of the nasal placode/pit differentiate into?
Neurosensory cells within the epithelium
The lateral walls of the nasal pit form blind-ended nasal sacs lined by surface ectoderm to form what?
Primitive nasal cavities
What membrane separates the oral cavity from the primitive nasal cavity?
Oronasal membrane
After the oronasal membrane ruptures during week 6, what primitive structure is formed allowing communication between the nasal and oral cavities?
Primitive Choana
What is the most common form of congenital nasal obstruction?
Choanal atresia
-failure of the oronasal membrane separating the nasal pits from the primitive cavity to break down during week 6
Why is Choanal Atresia especially dangerous?
“Normal” babies are nose breathers…
Babies with Choanal Atresia are mouth breathers.
This isn’t a problem for them until they are breastfeeding and are required to breath out of their nose while feeding.
Growth of what marks the formation of the definitive Choanae at the junction of the nasal cavity and the nasopharynx?
Secondary palate
(separate oral and nasal cavities)
What prominence forms the nasal septum?
Medial Nasal Prominences
What facial characteristics are affected by prenatal exposure to EtOH?
- Low nasal bridge
- Wide set eyes
- Short palpebral fissures
- Underdeveloped mandible (micrognathia)
- Thin upper lip
- Indistint philtrum
- Ear abnormalities, possible hearing impairment
- Short, up-turned nose
What is the difference between Anterior and Posterior defects of the face/palate?
- Anterior:
- involve upper lip, alveolar maxilla, & anterior palate
- e.g. cleft lip & cleft lip/anterior palate cleft
- Posterior:
- Inolved hard AND soft palate
- e.g. cleft palate
Fusion failure of what two things results in Anterior defects of the face/palate?
Maxillary prominences
&
Medial nasal prominence
Fusion failure of what two things results in Posterior defects of the face/palate?
Palatine Shelves (Lateral palatine processes)
&
Nasal septum/Posterior margin of Primary Palate
What factors influence/cause development failures that are factors in choanal atresia, nasolacrimal duct atresia, and Anterior/Posterior defects of the face/palate?
- Teratogenic factors (Alcohol, Dilantin, Vit A, Accutane, Corticosteroids)
- Genetic factors
- Excessive cell death during development/remodeling
- Excessively wide head
***More common in American Indian and Asian children.
