Lecture 2 - Development of the H&N Flashcards
What is the first evidence of face development in an embryo?
A depression appears in the ectoderm of the ventral aspect of the head, called the stomadaeum.
What are the five folds which appear around the stomadaeum to form the face?
Frontonasal prominence Maxillary prominences (2) Mandibular prominences (2)
What is the frontonasal prominence? What does it form?
Forms the forehead, bridge of the nose, upper eye and centre of the upper lip
What does the maxillary prominence form? Where is it derived from?
Derived from the 1st pharyngeal arch
Forms the middle third of the face, upper jaw, most of the lip and sides of the nose
What does the mandibular prominence form? Where is it derived from?
Derived from the 1st pharyngeal arch
Forms the lower third of the face, lower jaw and lip
What do the mandibular and maxillary prominences consist of?
Mesenchyme with a covering of ectoderm
Describe the formation of the nose
- Bilateral ectodermal thickenings called Nasal Placodes appear on the ventrolateral aspect of the frontonasal prominence
- Nasal placodes invaginate to form the nasal pits. The entrance to each pit is the future nostril.
- Medial and lateral nasal prominences around the nasal pits.
- The maxillary prominences grow medially and push the nasal prominences close together in the midline. Medial nasal prominences fuse in the midline.
Outline the formation of the palate
- Medial nasal prominences fuse in the midline, giving rise to the philtrum of the upper lip, median part of maxillary bone and the primary palate
- A palatal shelf grows from each maxillary prominence and fuse with each other and the primary plate.
- Fusion with each other forms the secondary plate
- Mandible grows large enough to allow tongue to drop out the way, allowing fusion
- Nasal septum develops as a midline down-growth and ultimately fuses with the palatal shelves
How is a cleft palate form?
Results from failure of one or both palatal shelves to reach the midline and fuse with its counterpart
How is a lateral cleft lip caused?
Failure of fusion of medial nasal prominence and maxillary prominence
How does a cleft palate form?
Palatal shelves fail to meet in the midline, combined with a failure of fusion of the medial nasal prominence
How does the development of the eye begin?
Out-pockets of forebrain make contact with overlying ectoderm, causing changes in it that form the optic placodes.
Optic placode then invaginates and pinches off.
What do the optic placodes become?
Lens of the eyes
When do the eyelids form?
Eyelids begin to develop at the end of the embryonic period (week 8). Then fused together during the second trimester and reopen in the third.
Where are the primordia of the eyes found intitally?
Positioned on the side of the head. As the facial prominences grow, the eyes move to the front of the face.
