As the placenta forms and the cytotrophoblast layer grows and extends, distal villous CYT differentiate to cell column CYT which eventually detach and invade deeply to the maternal decidua as interstitial<unk> s. These<unk> s anchor placental villi to the maternal decidua. Shallow implantation of<unk>  is associated with poor placentation and preeclampsia. Endovascular<unk> s are also major regulators of oxygenation during early placental development. Initially, they plug maternal spiral arteries to maintain hypoxia and prevent blood perfusion. This protects the fetus and placenta from oxidative stress during early development in the histiotrophic (glandular nutrition) stage. As fetal nutrition switches to the hemotrophic (blood-derived nutrition) stage,<unk>  plugs dissolve and perfusion of maternal blood begins, allowing further development of both the fetus and placenta.
Extravillous trophoblast
Cytotrophoblast
Syncytiotrophoblast
Athelia 
Hemangioblast
Neointima
Placental cotyledon
Stratified squamous epithelium