Biomedical Engineering Reference
In-Depth Information
Simultaneously, with neural crest cell migration, there is sequential
appearance of 5-6 pharyngeal arches; each arch having its own nerve,
blood supply and cartilaginous rod. The fi rst arch, the mandibular arch
forms the lower boundary of the developing stomatodeum together with
giving rise to the maxillary process, from its upper and back part (Figure
6.6). The bilateral maxillary processes make the roof and the posterior parti-
tion between the oral and the nasal cavities through its septal and palatine
processes, respectively. Derivatives of branchial arches also form an essen-
tial component in the craniofacial region. Branchial arches undergo bilateral
symmetrical fusion in the midline to form the mandible, the lower lip and
the tongue. This fusion which requires several different morphologic and
molecular events, implies disappearance of the covering epithelium which
could undergo migration, apoptosis and epithelial-mesenchymal transition
[48]. Interestingly, molecular investigation revealed that p53 coordinates
cranial neural crest cell growth, delamination and epithelial mesenchymal
transition by affecting gene expression at discrete developmental stages,
and that disruption of these processes could lead to craniofacial defects [49].
It is worth noting that appearance of the cartilaginous elements of the pha-
ryngeal arches together with their differentiation marks the beginning of the
second stage of craniofacial development (from about the 6th to 9th weeks
prenatal). During this stage, the cartilaginous cranial base or the chondrocra-
nium is formed. It provides the platform upon which the brain grows and
around which the face grows. Interestingly, the anterior and posterior cranial
bases, which grow independently, are derived from two distinct embryo-
logic origins, the neural crest and paraxial mesoderm, respectively [50].
Meckel's cartilage develops within the mandibular arch and extends
from the developing cranial base, in the region of the otic capsule, to the
1
T
2
3
4
H
Figure 6.6 SEM of developing mice head at the age of 13 days prenatal. The
mandibular arch forms the lower boundary/fl oor of the developing oronasal
cavity. 1, medial nasal process; 2, lateral nasal process; 3, maxillary process; 4,
mandibular process; T, tail region; H, developing heart; arrow, stomatodeum.
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