Studies on human aortic bifurcation. Part 1. Histo-architecture of the bifurcation.

The re-examination of the histo-architecture of the human aortic bifurcation was mainly focused in this study on the structure of its divider and the medial walls of its daughter vessels, both being presumably exposed to a higher mechanical strain as compared with other parts of the bifurcation. The microscopic structure of the divider is characterized by an arch-like course of its musculo-elastic structural components which follow the crescent shape of the dividers rim. Accordingly, in the central part of the divider the musculo-elastic bundles show a nearly horizontal course. They arise in both extensions and become more and more longitudinally disposed. This arch-like arrangement of the musculo-elastic core of the divider has been interpreted as a structural accomodation to the frontal impact of the axial pulsative blood stream upon the dividers rim. The tension which results from this impact is probably transferred by the dividers extensions into the aortic wall above the divider and in this way may be evenly distributed over the aortic tube. The medial wall of the bifurcation is characterized, in infants, by cushion-like thickenings of the arterial wall. These thickenings probably represent specialized structures which cope with a higher shear stress of longitudinal tension. In the asymmetrical aortic bifurcation of infants who had a single umbilical artery the cushion was present at the medial wall of the larger part of the bifurcation only, i.e. at the side of the single umbilical artery. This underlines the significance of the higher functional load for the development of this additional structure at the medial wall. The predominantly longitudinal arrangement of the musculo-elastic medial elements along the medial wall of the bifurcation in adolescents and young adults points to a considerable longitudinal tension to which this part of the arterial tube may be exposed.