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We found D: in early, and D: in late embryonic arteries and D: was also reported for lung vessels. Throughout this article, we consider the circulatory systems of mammals and birds as equivalent, because warmblooded species follow similar allometric relations. Preliminary data on the time course of SMC differentiation and our own data on indicate that this protein could be produced in proportion to T. We therefore assume that tensile stress in the wall, T. One should be aware that vascular wall tissue mass, MW, resembles a certain amount not only of material but also of energy for building and maintaining it.Therefore, MW must be included in a reasonable analysis of biological costs.Optimum conditions therefore may vary in different regions of the same individual, and at different times during ontogeny.Moreover, adult organisms may live in environments with afuent resources and hence may vary the design of their transport systems in a wider range than embryos, which are generally put under severe constraints with respect to resources of building materials and energy.This is bestillustrated by birds eggs, which are selfcontained with the exceptions of Glimepiride oxygen supply and incubation heat.We therefore expect that studying the vasculature of avian embryos may provide relevant data for discussing optimality conditions during circulatory organ development in other warmblooded animals.The extraembryonic vessels may be of particular interest, because the CAM tissues. While the blood contained in the CAM largely is returned to the chick before hatching, the vasculature itself must inevitably be abandoned.Apparently there would be a great primary advantage in the posthatching competition for food for the larger chicks that managed to incorporate a maximum of tissue and energy in their bodies, and waste as Glimepiride little as possible in the extraembryonic circulation.Similar considerations can be applied to the intraembryonic vascular system, because tissue volume used for the vascular wall is lost for parenchyma.While this seems obvious, it is interesting that this minimum can be solely dened by the constant wall stress condition.In a series of arterial diameter measurements during CAM development, we found D: before day and D: at days. These values could correspond to the initially low but rising perfusion pressures during maturation of the CAM.Nevertheless, we would like to speak of a minimumtissue law during vascular development that perfectly conrms predictions from allometry and is at concordance with actual measurements.Therefore, the basic biophysical aspects discussed in this article should pertain to vascular development in all warmblooded species.This is justied by the observation that birds and mammals are very similar with respect to their general metabolic capacity and design of their cardiovascular systems. On the molecular level, the similarity appears to be even greater, because essentially identical cytoskeletal and matrix proteins, growth factors and receptors, build and control the same types of tissues.This does not preclude that the design of the largest arteries may be different from that of the smaller ones, and that may be different in various parts of the system.for the required number of bifurcations.With respect to therapeutic approaches that are effective in different species, one never should forget that mice are not humans, because amongst other aspects of the allometric relations between body size and metabolism, which in turn is related to the physiology of angiogenesis.

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