Vasculature Growth - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 612

10.4 Vasculature Compartments

Hemangioblasts give birth to angioblasts that generate vascular endothelial cells.
During vasculogenesis, endothelial precursor cells in response to local signals
undergo proliferation, migration, differentiation, specification, and coalescence to
form the lining of nascent vessels. During angiogenesis, the vascular network is
remodeled into arteries, veins, and capillaries.

10.4.1 Lumen Size and Vessel Architecture

Whether blood flows with high or low flow rates and/or rapidly or slowly, vessels
widen or narrow, respectively. Blood vessels that carry a high-speed, large-volume
flow enlarge, whereas those with low-speed, small-volume flow regress. Local
features of hemodynamics thus direct formation of main perfusion vessels, as
endothelial cells respond to hemodynamical forces. Therefore, mechanical forces
generated by blood flow modify gene expression in the developing embryo. Blood
flow contributes to shaping a functional vascular architecture although vessel
identity and developmental patterning are genetically predetermined.
The vessel network is organized according to neighboring tissue growth and
structure. Vessel positioning depends on traction and compression forces exerted
by the growing tissues.

10.4.2 Cost Functions

Optimal design of vessel branching is based on cost functions that are the sum of the
rate at which work is done on blood and the rate at which energy is used, which are
supposed to be proportional to the vessel volume for each vessel segment [ 1182 ].
Other cost functions have been proposed based on the minimal total surface area of
blood vessels, minimal total volume, or the minimal total wall shear force on the
vessel wall, or minimal power of the blood flow.

10.4.3 Arteriovenous Differentiation

The primitive vascular network progressively matures with arteries, capillaries, and
veins [ 1183 ]. The specification of vascular cells in the different compartments
(arteries, capillaries, and veins) of the vascular circuit is not only determined by
applied mechanical forces and chemical factors (activators, inhibitors, and hypoxia),