Mess Andrea, Carter Anthony M
Museum of Natural History, Department of Research, Humboldt University Berlin, Invalidenstr. 43, DE-10115 Berlin, Germany.
Comp Biochem Physiol A Mol Integr Physiol. 2007 Dec;148(4):769-79. doi: 10.1016/j.cbpa.2007.01.029. Epub 2007 Feb 2.
The chorioallantoic placenta is an organ of gaseous exchange that exhibits a high degree of structural diversity. One factor determining oxygen transfer across the placenta, the diffusion distance, is in part dependent on the number of cell layers separating maternal from fetal blood. This interhaemal barrier occurs in three principal variants. The focus of this review is on determining how the barrier evolved in placental mammals. The analysis was based on current knowledge of placental structure, as far as possible using ultrastructural data, and on current views about the evolution of placental mammals, derived from molecular phylogenetics. We show that epitheliochorial placentation, the least invasive type, is a derived state and discuss factors that may have determined its evolution with reference to conflict theory, as applied to the allocation of resources between mother and fetus. It is not yet possible to determine which of the two more invasive types of placentation occurred in the last common ancestor of crown placentals. Depending on tree topology and taxon sampling, the result achieved is either endotheliochorial, haemochorial or unresolved. Finally we discuss other factors important to placental gas exchange and point to physiological variables that might become amenable to phylogenetic analysis.
绒毛膜尿囊胎盘是一种气体交换器官，具有高度的结构多样性。决定氧气跨胎盘转运的一个因素，即扩散距离，部分取决于分隔母体血液与胎儿血液的细胞层数。这种血间屏障有三种主要变体。本综述的重点是确定胎盘哺乳动物中这种屏障是如何进化的。分析基于目前对胎盘结构的了解，尽可能使用超微结构数据，并基于从分子系统发育学得出的关于胎盘哺乳动物进化的当前观点。我们表明，上皮绒毛膜胎盘形成，即侵入性最小的类型，是一种衍生状态，并参照冲突理论讨论了可能决定其进化的因素，该理论适用于母体与胎儿之间资源的分配。目前还无法确定在冠胎盘哺乳动物的最后共同祖先中出现的两种侵入性更强的胎盘形成类型中的哪一种。根据系统发育树拓扑结构和分类群抽样，得到的结果要么是内皮绒毛膜胎盘、血绒毛膜胎盘，要么是无法确定的。最后，我们讨论了对胎盘气体交换很重要的其他因素，并指出了可能适用于系统发育分析的生理变量。
