Reasons for Diversity of Placental Structure

摘要: Many early embryonic stages are nearly indistinguishable in different Eutheria. However, implantation and placental morphological types vary tremendously. A number of factors favor this conflicting diversity. 1. Whereas embryo development takes place the isolation amniotic cavity, extraembryonic membranes conceptus develop close association with uterus a genetically organism. 2. Early conditions for developing anaerobic whereas later efficient aerobic essential continued growth fetus. 3. Developing have potential to form two partially sequential placentas. The yolk sac can participate forming choriovitelline placenta, including an interhemal region, be adapted various non-respiratory functions as gestation proceeds. Development chorioallantoic placenta begins than but overlap before supplanting it. original occurs when is sufficiently small that neither its nutritional requirements nor respiratory needs burden maternal organism they gestation. Despite these developmental promoting methods definitive type consistent within most families indicating divergence structure accompanied evolution differences between groups.