Face, Jaws and Mouth Flashcards
What is the cephalic end?
Nasal placode?
Placode?
When are the basic features of the face developed/distinguishable?
Cephalic end: head end of a structure such as the trilaminar embryonic disc
Nasal placode: placodes that develop into olfactory organ for the sensation of smell located in the mature nose
Placode: area of ectoderm found at location of the developing special sense organs on the embryo
4th-10th week
4th week: disintegrating oropharyngeal membrane with prominences growing across
Stomodeum: primitive oral cavity, during 5th weej as maxillary processes grow, the stomatodeum will start to disintegrate
What is non-true fusion?
True fusion?
What is the stomodeum?
Non-true fusion: merging - the process by which a groove between two facial processes is eliminated
True fusion: fusion of separate processes e.g. medial nasal prominence with maxillary process
Stomodeum: first part of process when the temporary membrane disintegrates
- common oro-nasopharyngeal chamber
- primary palate: from fusion of medial nasal prominence, does not separate nasal and oral cavities
What happens at the end of 6 weeks?
7 weeks?
Week 10?
6 weeks: formation of a basic nose structure, gap between maxillary process and mesial nasal prominence
7 weeks: inferior tips of medial nasal processes expand laterally and inferiorly to join with intermaxillary process to form the intermaxillary segment –> true fusion, giving rise to future philtrum, primary palate and 4 incisors
10 weeks: fairly recognisable as a normal human face
What does each of the following contribute to the face?
- frontonasal:
- medial nasal:
- lateral nasal:
- maxillary:
- mandibular:
- frontonasal: forehead, bridge of nose
- medial nasal: philtrum of the lip, crest and tip of nose
- lateral nasal: alae of the nose
- maxillary: cheeks, lateral upper lip
- mandibular: lower lip
When does ossification begin in the mandible, maxilla, palate and nasal capsule?
What are the two methods of osteogenesis?
Ossification:
- 6-7th week - mandible
- 8th week - maxilla, primary palate, nasal capsule
Osteogenesis
- intramembranous ossification - concentric layers of osteoid
- endochondral ossification
What is cartilage for?
What are its 2 growth mechanisms?
- to form supporting framework of some organs such as airway, where it prevents collapse
- form articulating surfaces of the bones
- template for growth and development of long bones and most of the rest of the foetal skeleton
Interstitial growth: chondrocytes grow and divide, lay down more matrix inside the existing cartilage - developmental
Appositional growth: new surface layers of matrix are added to pre-existing matrix by new chondroblasts from the perichondrium
What is meckels cartilage?
Its fate?
Cartilage of 1st arch
- mandible preceded by meckels cartilage
- rod of cartilage around 6th week IUL
Fate: by week 10 the mandible is formed - acts as a template
Posterior extremity: forms malleus of inner ear and sphenomandibular ligament
How is the mandible formed?
What is osteogenesis?
- forms at start by intramembranous ossification - primary ossification centre between incisive and mental nerve - around 7 weeks IUL
- growth factors involved are VEGF, TGF beta 1 and BMPs
- ossification changes to endochondral ossification at the secondary cartilage sites
Osteogenesis: the process of laying down new bone material by osteoblasts
Name and describe when the mandibular secondary cartilages form and disappear:
Hw do they differ from primary cartilage?
Condylar: 10-12 weeks IUL
- disappears 20 years of age
Coronoid: 14-16 weeks IUL
- disappears before birth
Symphyseal: 16 weeks
- disappear 1st year after birth
- not part from primary cartilaginous skeleton
- fibrocartilage (not hyaline)
- appositional growth rather than interstitial growth
- produce endochondral ossification
