Vascular
Branching
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for distribution of fluid flow, in this case, blood
flow.
The simplest form
of branching is through bifurcation. A vascular structure of this form in
which the mother or source vessel
is
bifurcating into two daughter or
branching vessels, undergoes further bifurcation for generations. This is
known
as
the “open tree” structure. In such simplistic and idealistic
representation, each of the branching vessels are of the same lumen
diameter and the same vessel length. In addition, the angle of bifurcation
maintains the same. Thus, this uniform bifurcating structure represents a
basic fractal-like tree network model of the vascular system. Theoretical
studies based on bifurcation geometry have been numerous.
The
outcome from their predictions have been mixed. Good correlations have
been found for the extent of bifurcation vessel lengths and diameters,
much less for bifurcation angles (Zamir,
2000).
Vascular networks and branching geometry however are far more
complex in the cardiovascular system. Although bifurcation is the most
common form of vascular branching, trifurcation and multi-branching
junctions also occur in the mammalian vascular systems. In addition, the
uniformity in geometry is often not observed. That is, branching vessel
diameters and lengths, as well as branching angles can vary considerably.
Nevertheless, bifurcation predominates in vascular branching structure.
Examples of the vascular branching structure that do not obey the
straight bifurcation scheme is readily visible by looking
at
the aorta and
its branches. The aortic arch is curved and has many branches, none of
which maintains the same vessel diameter and length in these branching
arteries, such as the brachiocephalic and the subclavian. However, the
two common carotid arteries represent a long, uniform, bifurcating
structure. Taking the direction along the length of the thoracic aorta
through abdominal aorta, we observe many branches that come off the
aorta at almost right angles, far from those at the aortic arch or the aorto-
iliac junction. The aorta however, provides another kind of branching
structure for efficient transport.
For instance, the aorta itself, though
tapered maintains
a
larger trunk diameter in comparison to its branching
arteries and its mere length ensures fast delivery of blood to its branches.
This represents another scheme of branching structure.
