Development of Orofacial Structures Dennis Flashcards
What is Intramembranous ossification
Mesenchyme produces osseous tissue without the use of cartilage formation. The mesenchyme will condense and become vascular and differentiate into osteoblasts and deposit osteoid. Osteoblasts become trapped in lacunae and become osteocytes.
What is endochondral ossification?
Bone formation occurs using the cartilage model. Primary ossification centers first appear in the diaphysis and then chondrocytes become hypertrophic and eventually calcify. Meaning the chondrocytes die and then replaced by bone
What is the order of cartilaginous neurocranium formation?
Occipital bone, body of sphenoid and finally ethmoid bone
what makes up the membranous neurocranium?
Calvaria frontal and parietal bones which form through intramembranous ossification and are connected by sutures
What is the viscerocranium?
Bones that make up the face
What portions of temporal bone form cartilaginous
Petrous and mastoid part
Relate cartilaginous viscerocranium to the PA’s.
PA1: malleus and incus
PA2: stapes styloid process and lesser horn hyoid
PA3: greater hyoid horn
PA4: cartilages fuse to form laryngeal cartilages
What is Scaphocephaly?
Premature closure of sagittal suture and cranium becomes long narrow and wedge shape. Type of craniosynostosis
What is Brachycephaly?
Premature closure of the coronal suture, creates a high tower like cranium
What is Plagiocephaly?
One side of the coronal suture closes prematurely so the cranium is asymmetric
What is trigonocephaly?
Premature closure of frontal suture which will cause malformation of frontal and orbital bones
When does the facial primordia appear?
4th week
What arches are the maxillary and mandibular prominences from?
1st arch
The facial primorida is separated from cavity of primordial pharynx by _____.
bilaminar membrane- Oropharyngeal membrane
When does the oropharyngeal membrane rupture?
26 days
What are the derivitives of the FNP and what cells make it up?
Frontal portion of the forehead
Nasal portion forms the rostral boundary of the stomodeum and nose tip
NCC from forebrain and midbrain
What cells populate the MXP and MDP?
NCC from midbrain and hindbrain
What are the first parts of the face to form?
The lower components such as the lower jaw and lip
What are nasal placodes and when are they formed by?
Formed by end of fourth week on the inferolateral parts of the FNP
They are bilateral oval thickenings of the surface ectoderm & are primordia of the nasal epithelium
When the placodal edges proliferate what do they produce?
Medial and lateral nasal prominences
The placodes are now in depressions called nasal pits
What do nasal pits form?
nostrils and nasal cavities
What do the lateral nasal prominences form?
alae of the nose
Where do maxillary prominences grow?
Medially toward each other as well as to the median nasal prominences
which results in movement of the MNP to the midline
What separates the LNP from the maxillary prominence?
Nasolacrimal groove
When does the MXP and LNP merge at the nasolacrimal groove?
by the end of the sixth week
Medial nasal prominences merge with maxillary and lateral nasal prominences between what weeks? What does this result in?
7-10 weeks
Continuity of upper jaw and lip and separation of nasal pits from stomodeum.
As the MNP’s merge they form ____. What does it form?
Intermaxillary segment which makes the premaxillary part of maxilla, primary palate, core of philtrum of upper lip while surface of lip is from MXP
What forms the maxillary prominences?
Most of upper lip, maxilla and secondary palate
Mesenchyme/mesoderm in the PA2 forms?
Facial muscles and is innervated by facial nerve
PA1 mesenchyme/mesoderm forms?
Muscles of mastication trigeminal nerve
What causes the nasal placodes to deepen?
Proliferation of facial mesenchyme
Placode –> Nasal Pits –> Primordial nasal sacs
How do the primordial nasal sacs grow in relation to the forebrain? How are they separated from the oral cavity?
Dorsally and ventral to the forebrain and separated by the oronasal membrane which ruptures around week 6 to connect the cavities
Describe palatogenesis timeline
Develops from the primary and secondary palates in 2 stages. It begins around week six and is finished by 12 weeks. There is a 3 week critical period between 6 and 9 where palate malformations can occur.
What forms the median palatine process/primary palate? What will it form?
merging of MNP forms it and it is a wedge shape mass of mesenchyme between the maxillary prominences and forms the premaxillary prat of the maxilla
How does the secondary palate form?
Develops in the 6 week from lateral palatine processes from the mesenchyme of the MXP.
Describe the process of the secondary palate formation.
Palatine processes extend inferiorly on each side of the tongue. Mandible elongates pulling tongue forward and down in the mouth
Palatine processes flip horizontally above the tongue around 7-8 weeks.
Describe the formation of the final palate?
Bone gradually develops into primary palate forming premaxillary part of maxilla with the incisors. Bone extends from maxillae and palatine bones into lateral palatine processes to form hard palate. Soft palate and uvula are from the posterior portion which does not ossify
Describe cleft lip.
Extends through the upper lip and it is a lack of fusion between maxillary prominences and median nasal prominences .
Describe cleft palate.
Clefts of secondary palate to incisive fossa. Can involve uvula &/or hard and soft palates. It is a lack of fusion btw palatine process with nasal septum and lateral palatine process with median palatine process
What is the nasal septum derived from?
Down growth from internal parts of merged median nasal prominences
When does fusiohn of nasal septum and palatine processes begin?
anteriorly in the 9th week and posteriorly in the 12 week
What is the first indication of tongue development?
Median lingual swelling at the end of fourth week
Describe the lateral lingual swellings.
AKA distal tongue buds, develop on each side of the medial lingual swellings. They rapidly proliferate merge and overtake the median swelling. The tongue buds will result from proliferation of mesenchyme in ventromedial parts of PA 1
what forms the copula?
Ventromedial parts of PA2 fuse to form it
What forms the hypopharyngeal eminence?
OA3 and PA4
What makes up the pharyngeal part of the tongue?
Copula and hypopharyngeal eminence as they come from pharyngeal arches
Tongue musculature is derived from what?
Myoblasts of occipital myotomes also accompanied by CN 12 to innervate the tongue
What is glossoschissis?
incomplete fusion of lateral lingual swellings- bifed tongue
Ankyloglossia?
frenulum is short and extends to tip of tongue, can impact feeding
Macroglossia?
excessively large tongue generalized hypertrophy seen in infants with down syndrome
Microglossia
small tongue (rare) and associated with micrognathia
