ABSTRACT
The vasculature, which is a complex and highly integrated system of conduits, is
deceptively simple from the standpoint of the cellular composition of each
individual blood vessel. All vessels of the entire vasculature are composed, at
most, of only two cell types, the endothelial cell and the vascular smooth muscle
cell. Vessels of all sizes are also surrounded by the specialized supporting cells
and structures known as the adventitia. The space around capillaries, which
varies greatly from tissue to tissue, also contains an additional cell, the pericyte,
which is not contractile and about which relatively little is known. Large mus-
cular arteries, elastic arteries, and veins are surrounded by adventitial fibroblastic
cells and a great number of other specialized structures, including nervous tissue
and, in the case of large elastic arteries, vasa vasorum. Thus, while the basic
cellular components of blood vessels per se are simple, the characteristics of
these elements vary greatly from vessel to vessel and the integration of varying
types of blood vessel with adjacent structures is quite complex.
