It is well known that arteries respond to variations in loads. Changes in the endothelial fluid shear stress or luminal pressure result in both short term (smooth muscle contraction or relaxation) and long term (muscle growth and proliferation, as well as scleroprotein remodeling) adaptations in order to return the artery to the homeostatie state. We have developed a thick-walled orthotropic model of the developing and mature artery using a rule of mixtures approach to delineate the effect of each vascular constituent. This model incorporates both short and long term growth and remodeling of the vascular smooth muscle cells and collagen. The model reproduces arterial development from vasculogenesis through maturation, as well as the acute and chronic changes in the artery due to sudden perturbations in pressure or flow rate.