Embryology - Development of mouth and face Flashcards
When is the stomadeum present?
Third week:
- SOmites appear and the buccopharyngeal membrane breaks down.
When the embryo is 3mm long and in its 4th week what happens?
The frontonasal process and the beginning of mandibular and hyoid arches appear.
When do teeth start forming?
Six weeks.
How big is the embryo at 6 weeks?
12mm long.
When does calcification of the first dentine occur?
In the 5th month, followed closely by enamel.
What bounds the stomodeum?
Mandibular arch.
What does the mandibular arch produce?
- Floor of the mouth.
- Lower jaw.
- Lower lip.
- Two maxillary processes.
What is the mandibular arch’s cranial boundary?
Forebrain capsule.
What does the forebrain capsule develop into?
Frontonasal processes.
How is the frontonasal processes identified?
Two nasal pits:
1. Median processes.
2. Two lateral nasal processes.
How is the median process characterised?
By a pair of convex globular processes.
What happens to the lateral nasal processes?
They unite with the globular processes to encircle the nostril.
What does the maxillary and lateral nasal processes encircle?
The eye - they meet together alon the line of nasolacrimal duct.
Where on the facade does the maxillary process unite?
In the midline below the nostril. To produce the whole of the upper lip and the maxillae.
What does the frontonasal processes produce?
Pre-maxilla - which is covered over by medial extensions of the maxilla in man.
How is the upper part of the face formed?
By fusion of the frontonasal and maxillary processes. However, it’s just a mask at first, as the nasal septum and palate have yet to be completed.
Where does the developing tongue lay?
Against the floor of the cranium.
How does the nasal septum form?
A midline flange grows down from the base of the forebrain capsule (mesenchymal precursor of the skull).
What grows from each maxillary process?
Flange - palatial process grows medically across the dorsum of the tongue.
What happens when the nasal septum and the two palatal processes meet?
They unite from before backwards, they separate the nasal cavities from each other and also separate the cavities from the mouth.
What forms the nasal capsule?
Mesoderm.
When does chondrification of the nasal capsule occur?
By the 6th week.
What also occurs at the 6th week?
THe nasal walls and hard palate are outlines by a thin layer of hyaline cartilage.
When does ossification of the hyaline cartilage in the nasal capsule begin?
After 6 weeks.
What happens to the hyaline cartilage in the upper part of the wall of the nose?
The hyaline cartilage is replaced by bone.
What happens to the hyaline cartilage in the lower part of the septum and the hard palate?
There is deposition of membrane bone on each surface of the hyaline cartilage.
What becomes of the hyaline cartilage after there is deposition of membrane bone on each surface?
It becomes sandwiched between two lawyers of membranous bone and is not absorbed until some time after birth.
What innervates all of these structures (inside and outside)?
Fifth cranial nerve - trigeminal nerve.
What supplies the frontonasal process and its derivatives?
Ophthalmic division of the trigeminal nerve.
What supplies the maxillary process and its derivatives?
Maxillary division.
What supplies the lower jaw?
Mandibular division of the trigeminal nerve.
What are the most commonest abnormalities in mouth development?
- Cleft palate.
- Hare lip
What is the occurrence of cleft palate?
1 in 1000.
What is the occurrence of Harelip?
1 in 2500.
What is harelip?
Where the defect runs almost always lateral. The cleft runs down from the nostril.
How does harelip occur?
The median part of the lip is derived from the opposite maxillary process or from the frontonasal process.
How does cleft palate form?
The two palatal processes unite with each other (and with the nasal septum) from before backwards. There is arrest of this union.
What happens in severe cleft palate?
There is no union from the uvula to the gum margin. It always runs between premaxilla nd maxilla nad involves the jaw between the lateral incisor and canine teeth.
What happens in severe cleft palate?
There is no union from the uvula to the gum margin. It always runs between premaxilla nd maxilla nad involves the jaw between the lateral incisor and canine teeth.
What happens in severe cleft palate?
There is no union from the uvula to the gum margin. It always runs between premaxilla nd maxilla nad involves the jaw between the lateral incisor and canine teeth.
What happens in severe cleft palate?
There is no union from the uvula to the gum margin. It always runs between premaxilla nd maxilla nad involves the jaw between the lateral incisor and canine teeth.
What is a less common facial defect?
Facial cleft forms along the line of nasolacrimal duct, when there is failur of fusion of the lateral nasal process with the maxillary process.
