196
Dynamics
of
the Vascular System
in Table
7.1.
Data from more than one hundred mammalian species
show that the red blood cells are of similar size and that there
is
no single
mammal has a red cell diameter over 10 um. This suggests the structural
sizes of the capillaries are in the same order of magnitude in these
mammals. It should be noted however, that the structures and functions
of the endothelial cells lining the capillaries may differ, depending on the
microvascular bed of a particular organ they serve. In addition, the
topological branching structures of the different microvascular beds are
unique for each organ. For instance, the pulmonary microcirculation has
an entirely different vascular tree structure as compared to the coronary
microcirculation, or that of the cerebral microcirculation.
Table 7.1.1
:
Diameters
of
red blood cells (RBC)
of
some mammalian species.
Species
Body weight
(kg)
RBC
Dismeter (um)
Shrew
.o
1
7.5
Mouse
.20
6.6
Rat
SO
6.8
Dog
20
7.1
Man
70
7.5
Cattle
300
5.9
Horse
400
5.5
Elephant
2000
9.2
The arteriole (10-125 pm) has smooth muscle cell layers in its wall
with the nerve connection to its outermost layer. Even the terminal
arteriole still has a single layer of smooth muscle cells.
A
meta-arteriole
has a discontinuous layer of smooth muscle cells. Pre-capillary sphincter
is the last smooth muscle cell at the end
of
terminal arterioles.
Similarly, there are post-capillary venules, and collecting venules (1 0-50
pm) and small collecting veins which already has intima endothelial
layer, the media with smooth muscle layers.
7.1.2.
The
Capillary Circulation
The extensiveness of the organizational structure of the network of
capillaries is necessary for efficient cellular transport and diffusion
