Development of the Skeletal System
EMBRYOLOGY: Note #1.
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IV) INTRAMEMBRANOUS VS ENDOCHONDRAL
These two processes of bone formation
are also based
on gene expression
Intramembranous Ossification
o Mesenchymal cells have genes
which stimulate the
formation of bone tissue
o The expression of the CBFA and RUNX2 genes lead
to the production of osteoids and other proteins which
are responsible for the phenotypic development of
osteoblasts
Endochondral Ossification
o The Sox9 gene is responsible
for the conversion of
mesenchymal cells to chondrocytes
Figure 9. Types of Ossification
V) REVIEW QUESTIONS
1) Which two structures are important for the
development of the skull?
a) Occipital somites
and neural crest cells
b) Occipital somites and AER
c) Cervical somites and neural crest cells
d) Cervical somites and AER
2) Which of the following was NOT developed through
endochondral ossification?
a) Sphenoid bone
b) Ethmoid bone
c) Parietal bone
d) Occipital bone
3) The first pharyngeal arch differentiates into which of
the following structures?
a) Frontal bone
b) Zygomatic bone
c) Stapes
d) Clavicle
4) Which part of the somite will differentiate into the
vertebral bodies?
a) Dermatome
b) Myotome
c) Sclerotome
d) All of the above
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