Week 3.0 - Development of the nose and face Flashcards
What are neural crest cells?
-Specialised population of cells, present throughout the body, that arise within the lateral neuroectoderm
What happens to neural crest cells upon fusion of the neural tube?
-Displaced into mesoderm
What is the palpebral fissure?
-Spece between eyelids
What is the philtrum?
-Groove in upper lip
From where is the facial skeleton derived?
-Neural crest of first pharyngeal arch
Where do MoM arise from?
-Mesoderm of 1st Ph Arch
Where do muscles of facial expression arise from?
-Mesoderm of 2nd Ph Arch
What contributes to the facial primordia?
- 1st pharyngeal arch
- Frontonasal Prominence
From where does the primordia of the eyes originate
-Frontonasal prominence
What is stomatoduem?
-Buccopharyngeal membrane -> primordia of the mouth
State the external features which arise from the frontonasal prominence
- Forehead
- Bridge of nose
- Nose
- Philtrum
- Primary palate
State the external features which arise from the maxillary prominence of the 1st pharyngeal arch
- Cheeks
- Lateral upper lip
- Lateral upper jaw
- Secondary palate
State the external features which arise from the mandubular prominence of the 1st pharyngeal arch
-Lowet lip and jaw
Where do the nasal placodes first appear? How?
- Frontonasal prominence
- Thickening of the ectoderm
Describe the formation of the nose
- Nasal placodes appear on FNP
- Cells begin to differentiate and the placodes sink to form nasal pits
- Medial growth of maxillary prominence pushes nasal prominence close together in midline
- Maxillary prominences fuse with nasal prominences
- Further maxillary prominence growth pushes medial nasal prominences together which then fuse
What is the intermaxillary segment during facial development?
- Formed by fusion of medial nasal prominences
- > philtrum, upper jaw and primary palate
What is the main section of the definitive palate?
-Secondary palate during development
How is the nasal cavity initially separated from the oral cavity in facial development?
-Oronasal membrane
From where does the primary palate arise?
-Intermaxillary segment
From where does the secondary palate arise?
-From the palatal shelves from the maxillary prominence
Describe the development of the secondary palate
- Palatal shelves grow downwards into the oral cavity on each side of the developing tongue
- Mandible grows large enough to allow tongue to drop downwards
- Palatal shelves grow towards each other and fuse in the midline as the maxillary prominence develop
Describe formation of nasal septum
-Grows down the midline and fuses with palatal shelves
Why are the lip and palate described as being of dual origin?
- Primary palate and philtrum from intermaxillary segment from medial nasal prominences (FNP)
- lip and Secondary palate from maxillary prominence
What is a lateral cleft lip?
-Failure of fusion of the medial nasal prominence and the maxillary prominence
What is a cleft palate?
- Failure of palatal shelves to meet in the midline
- Can either involve primary palate only or both primary and secondary palates
Describe the formation of the eyes in facial development
- Out-pocketings of forebrain grow out to make contact with overlying ectoderm of FNP forming the optic vesicle
- Contact with ectoderm induces lens placode development due to thickening of ectoderm
- Lens placode invaginates, with the optic vesicle, and pinches off forming the lens vesicle, the two surface of optic vesicle fuse together to form retina, surrounding the lens vesicle.
Explain the positioning of the eyes in development
- Primordia are positioned on the side of the head
- As facial prominences grow, the eyes move to the front of the face
Describe the formation of the external ear
- External auditory meatus develops from 1st pharyngeal cleft
- Auricles develop from proliferation of the 1st/2nd Ph arches surrounding the meatus
Descibe the positioning of the external ear
- Primordia in the neck
- As mandible grows the ears ascend to the side of the head to lay in line with the eyes
Describe the common facial features of fetal alcohol symdrome
- Underdeveloped jaw
- Flattened face
- Smooth philtrum
- Small palpebral fissures
- Short height
Why is alcohol so dangerous to the developing embryo?
-Freely crosses the placenta and interferes with neural crest migration and CNS development
What 3 things drive development of the face?
- Expansion of neural tube
- Appearance of cranial gut tube and outflow of heart
- Development of sense organs
