Abstract
The placenta is a transient vascular organ that enables nutrients and blood gases to be exchanged between fetal and maternal circulations. Herein, the structure and oxygen diffusion across the trophoblast membrane between the fetal and maternal red blood cells in the feto-placental vasculature system in both human and mouse placentas are presented together as a functional unit. Previous models have claimed that the most efficient fetal blood flow relies upon structures containing a number of ‘conductive’ symmetrical branches, offering a path of minimal resistance that maximizes blood flow to the terminal villi, where oxygen diffusion occurs. However, most of these models have disregarded the actual descriptions of the exchange at the level of the intermediate and terminal villi. We are proposing a ‘mixed model’ whereby both ‘conductive’ and ‘terminal’ villi are presumed to be present at the end of single (in human) or multiple (in mouse) pregnancies. We predict an optimal number of 18 and 22 bifurcation levels in the human and the mouse placentas, respectively. Wherever possible, we have compared our model's predictions with experimental results reported in the literature and found close agreement between them.
Highlights
The placenta is an effective reporter of information about placental and fetal exposures and their developmental consequences [1]
Because the measurement of dft is challenging and requires a detailed analysis of the vasculature system in order to define dft, we utilize the modelling assumption described by [28] to derive the optimal number of bifurcation levels that lead to the easiest fetal blood flow, as well as oxygen transfer through the vasculature system
We focused on the optimization of both human and mouse placental vasculature systems as follows
Summary
The placenta is an effective reporter of information about placental and fetal exposures and their developmental consequences [1]. After estimating the optimal number of bifurcation levels yielding the minimum total oxygen transfer resistance for mass transport between the fetal and maternal blood in the human and mouse placentas, we evaluate some specific parameters, such as optimum oxygen volume flow rate through the vasculature system and the fetal capillary diameter, that are usually difficult to measure experimentally. There are some distinctions between our proposed model and the model reported by [29] including: (1) the method to define the diffusive flux resistance in the vasculature system, (2) the calculation, in detail, using the Hill equation and experimental parameters, of the concentration of oxygen dissolved in the fetal blood plasma and bound to haemoglobin, (3) the proposed model considers the number of cotyledons and fetal capillaries in both human and mouse placenta and (4) even. These bifurcation resistances can be neglected because the values are very small in relation to channel resistances
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