Biomedical Engineering Reference
In-Depth Information
Table 11.1.
Repair stages and timing (Source: [
1377
]).
Period
Events
Day 1
Hemostasis
Vasoconstriction
Cell influx (neutrophils)
Week 1
Vasodilation; inflammation
Cell influx (macrophages, lymphocytes, fibroblasts)
Growth factor signaling; cell proliferation
Collagen deposition
Month 1
Remodeling
Collagen crosslinking
11.1
Organogenesis
Organogenesis during embryonic development relies on differentiation and replica-
tion of stem and progenitor cells down to terminal differentiation and proliferation
of differentiated cells. Organogenesis is achieved in sequential stages from the
formation of an anlage, invagination of the primary bud, reiteration into various
branches, to organization into specific proximal and distal structures.
11.1.1
Ecto-, Endo-, and Mesoderm
Organogenesis is the process by which the ecto-, endo-, and mesoderm develop into
organs (between week 3 and 8 of in utero life; Table
11.2
). Regulators control the
formation of spatial patterns as well as timing of patterning events.
Differential adhesion and tension as well as directed cell migration determines
progenitor sorting.
Differential adhesion hypothesis
of organization of cell layers
during the development of embryonic tissues states that in 2 cell populations
that aggregate the more cohesive one (with the stronger homotypic adhesion)
distributes in the middle and the less cohesive one on the outside [
1379
,
1380
].
The spreading of one embryonic tissue over another and the formation of intertissue
borders are supposed to behave like immiscible liquids. Adhesive forces between
aggregated cells play the same role in cell sorting as intermolecular attractive forces
in liquid surface tension. Distinct expression of cell adhesion molecules, especially
cadherins, regulates histotypic sorting out of cells of embryonic tissues when cells
are intermixed.
Differential surface contraction theory
of morphogenesis states that cell cortical
tension developed by the cytoskeleton rather than adhesion between cells generates
cell sorting [
1381
]. In addition, signaling between mesenchymal and epithelial cells
Search WWH ::
Custom Search