|
The
chordamesoderm induces the formation of |
Neural
crest. From the ectoderm, due to the interactive inductive stimuli between cells separated by a distance for a short time, neural crest cells are formed. |
|
The
set of cells that arise from the ectoderm along the lateral margins of neural plate are the |
Neural
crest. These cells undergo migration at the time of neural tube closure. |
|
Of
all the hard tissues of oral cavity the one that is non-neural crest in origin is the |
Enamel.
Enamel is derived from inner enamel epithelium that arises from oral ectodermal lining. |
|
Migrating
neural crest cells in the upper facial region forms |
The
entire mesenchyme. In the lower facial arch region the migrating neural crest cells surround the pharyngeal arch to form the bars, whereas in the upper facial region they ramify and form the entire mesenchyme. |
|
Most
of the sensory neurons of cranial sensory ganglia originate from |
Neural
crest tissues. Only in the trunk they originate from neural crest cells. In head most of them are derived from surface ectoderm. |
|
The
neural crest cells aggregate around the neural tube where the |
Sensory
ganglia of 5th, 7th, 9th and 10th Cranial nerve form |
|
The
condensed masses of cells of mesodermal origin adjacent to neural tube are |
Somites.
They give rise to muscle cells |
|
The
first formed supporting cells of blood vessels from the ectomesenchyme are the |
Pericytes
|
|
The
growth and fusion of upper facial prominences produces the |
Primary
and secondary palate |
|
Inductive
influences originating from forebrain initiate the formation of |
Nasal
placodes. Before the neural crest cell migration, the surface ectoderm lies in apposition to portions o developing forebrain. After this induction, the mesenchymal tissues separate the ectoderm from developing forebrain. |
|
The
“Placodes” are thickenings of |
Ectoderm.
These ectodermal thickenings give rise to various vital sense organs such as the lens and olfactory epithelium. |
|
The
nasal placodes will give rise to |
Sensory
epithelium of olfaction |
|
The
medial and lateral nasal prominences contact each other |
Below
nasal pit. With this contact the epithelium breaks down so that the mesenchyme becomes continuous. |
|
In
human embryo the medial and lateral nasal prominences fuses during |
Fifth
week IUL |
|
Initial
nasal passage is formed near the fusion of medial and lateral nasal placodes by |
Accumulation
of fluid between epithelial cells. This fluid accumulation causes the epithelial cells to separate creating a passage at about 5th week of intrauterine life and connects the olfactory pit with the roof of primitive oral cavity. |
|
The
medial and lateral nasal prominences fuse and give rise to |
Primary
palate |
|
The
roof of the anterior part of primitive oral cavity is formed by |
Primary
palate |
|
The
primary palate gives rise to the |
Part
of upper lip, anterior maxilla and upper incisors |
|
The
secondary palate arises from the |
Medial
edge of maxillary prominences |
|
The
palatal shelves growth direction is |
Downward
beside tongue. This growth occurs beside the tongue when it probably fills partially the nasal cavity. |
|
In
humans, the palatal shelves fuse at about |
Ninth
week intrauterine life |
|
Alteration
in the epithelium at the medial edge of the palatine shelves before its fusion causes |
Cessation
of cell division; Raise in cAMP; Increased surface adhesive glycoprotein. The cessation of cell division is mediated by a various biochemical pathways. In addition apoptosis is also noted. |
|
During
secondary palate formation the palatal shelves, in anterior region, are brought to horizontal position by |
Rotational
movement |
|
During
secondary palate formation the palatal shelves, in posterior region, are brought to horizontal position by |
Remodeling
and rotational movement. Shelves are incapable of elevation till tongue is withdrawn. This occurs with the help of contractile elements. Remodeling brings about change in shape. |
|
The
pituitary gland develops from |
Ventral
forebrain and oral ectoderm. As a result of inductive interaction between the ventral forebrain and oral ectoderm and is hence derived from both the tissues. |
|
In
humans, the total number of visceral arches is |
Six
|
|
Mesodermal
core of each visceral arch is primarily concerned with the formation of |
Vascular
endothelial cells |
|
In
humans, the rudimentary pharyngeal arch is |
Fifth
|
|
The
proximal part of the first visceral arch forms |
Maxillary
prominence |
|
The
mesoderm of mandibular and hyoid arch gives rise to |
5th
and 7th Nerve musculature |
|
The
mesoderm of 3rd and 4th arch gives rise to |
9th
and 10th Nerve musculature |
|
The
crest mesenchymal cells of visceral arches give rise to the |
Skeletal
components; Connective tissues; Tongue |
|
In
humans, the tongue formation initiates in the |
Ventral
floor of pharynx |
|
During
development, the covering of tongue is |
Anterior
two third ectoderm and posterior one third endoderm |
|
Mesenchymal
component of anterior two thirds of human tongue are derived from |
Third
arch mesenchyme |
|
The
lateral extension from the inner groove between first and second arch gives to |
Eustachian
tube |
|
The
pinna is formed from |
Both
first and second arch |
|
The
embroyonic period of human lasts till |
Eighth
week intrauterine life |
|
The
most common defect of embryonic facial development is the |
Cleft
of primary and or secondary palate |
|
Excess
doses of vitamin A given to mother during pregnancy causes defects similar to |
Treacher-Collin
syndrome |
|
The
result of persistence of tuberculum impar after tongue formation is suggested to cause |
Median
rhomboid glossitis. This is an earlier hypothesis which is disagreed now and infection with candidal organism is the cause suggested now. Improper or incomplete union of the lateral lingual processes produces scrotal tongue and partial union produces the bifid or cleft tongue. Agenesis will be produced by the non formation of the lingual processes. |
Prof. Rooban Thavarajah
Oral and Maxillofacial Pathologist
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