Figure 2.

Schematic representations of hemochorial placentation sites of the human and rat highlighting similarities in structural organization. The extravillous trophoblast column and junctional zone are homologous structures of the human and rat, respectively. These structures are the sources of trophoblast cells that invade deep into the uterus. The villous and labyrinth compartments are homologous structures of the human and rat, respectively, and represent the site of maternal-fetal exchange. Histological organization of the villous and labyrinth compartments are defined as hemomonochorial and hemotrichorial, respectively.