Hematopoietic Stem Cell Development, Niches, and Signaling Pathways
Mouse placenta development. (a) At E3.5 of early embryogenesis, blastocyst is formed, containing inner cell mass located at one side of the blastocoelic cavity and outer layer (trophectodermal epithelium) which give rise to the placenta. (b) Between E7.5–E8.25 mesodermal precursors originating from the primitive streak grow into the allantois (light grey) which then develops toward the ectoplacental cone (dark grey). (c) Chorioallantoic fusion between the allantoic and chorionic mesoderm at E8.5. After that, Chorionic villi and vasculature are formed producing and generates extensive villous branching called labyrinth. (d) At E11.5, umbilical cord is fully formed to connect the placenta with fetus where fetomaternal bloods circulate. (e) Cross-section of the placenta at E12.5 showing the chorioallantoic mesenchyme lies cover the placenta labyrinth with fetal vessels lined by fetal endothelium (dark vessels with lumen) and trophoblast lined by maternal blood spaces (grey vessels surrounded by dark trophoblasts). al, allantois; ch, chorion; am, amnion; epc, ectoplacental cone; ys, yolk sac; psp, para-aortic splanchnopleura; da, dorsal aorta; ua, umbilical artery; va, vitelline artery; fl, fetal liver (modified from ).
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