Biomedical Engineering Reference
In-Depth Information
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Habituation
Model
Fig. 4 Three speculative models explaining how mechanical and chemical signals become
integrated in specifying artery and vein. Morphogenetic, Habituation, Integrative models are proposed
5.1 Morphogenetic Model
Based on this model, genetic regulatory mechanisms that determine arterial and
venous phenotype provide information necessary for each endothelial cell type to
lay themselves in specific spatial positions (Fig. 4 a). Such mechanisms allow them
to be positioned at the right place relative to each other and among arteries and
veins, thus leading to the establishment of specific geometrical arrangements of the
vascular system consisting of arterial and venous wiring.
According to this model, endothelial cells sense chemical and mechanical cues
in their microenvironment. Upon sensing these signals, endothelial cells respond
by expressing arterial and venous genes that code proteins necessary for estab-
lishing their spatial organization. Both arterial and venous endothelial cells are to
be laid down correctly among themselves and also relative to each other. Their
position in the body relative to the heart is also critical for their required physi-
ological functions. Furthermore, their positions relative to body axis (left-right,
anteroposterior, dorsoventral, etc.), as well as those within each organ, are also
essential for the whole body and organ functions and development [ 58 , 59 ].
In fact, it has been implicated that EphrinB2 and EphB4, respective arterial and
venous markers, function as a ligand-receptor system that mediates cis- and trans-
interactions necessary for establishing normal arteriovenous architecture of the
vascular system [ 60 ].
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