Figure 2.

Representative analytical model. (a) Feto-placental vasculature system. (b) Fetal capillary system (note that this diagrammatic representation of villous vasculature ignores the existence of arterioles and venules and treats the villous as having a single vessel). (c) The system resistivity chart with respect to the oxygen transport. The fetal vessels are assumed to be cylindrical channels where the Hagen–Poiseuille equation can be applied; the fetal capillary is assumed to have a spherical shape; and the vasculature system is assumed to be symmetrical. Here, R, L, d and N represent the total resistance, the length and diameter of the vessels, and the number of bifurcation levels, respectively. The pictures are not to scale.