The mechanisms that regulate arteriolar diameter and hence blood flow through the arteries involve both local (e.g. release of chemical substances into tissue) and systemic factors, (e.g. stimulation of the baroreceptors and the vasomotor center). The arterial system as a whole is never static but continuously undergoes structural changes and adaptations that permit the organism to respond to changing requirements for blood supply.
Even at birth, arteries vary in structure and in distribution depending upon the hemodynamic conditions under which they operate. Arteries continue to change with maturation and advancing age of the individual, changes that are continuously affected by extrinsic as well as intrinsic factors; in the process of adapting to environmental stimuli, structural changes occur at particular sites, and the gross pattern of vascular distribution to an organ or body part may undergo considerable change, as in the development of collateral circulation.
Evidence suggests from human and experimental observations that the rigid classification of the various elements that form the arterial wall into definite "species" of cells has to be abandoned in favor of a far more versatile view of the cellular configuration of the arteries. It seems that these cells are not irrevocably specialized but, rather, that they can assume more than one function when the need arises. For example, a muscle cell will not only contract upon stimulation but, under certain conditions, it could also phagocytizes lipid and even produce collagen or elastic fibers - a potential that might have a bearing on the formation of atherosclerotic lesions.