Trofoblast

Trophoblast is a layer of flat to cuboidal cells forming the outer layer of the epithelium of the blastocyst (outer cell mass), which differentiates into the amniotic envelope and the placenta (extraembryonic tissue of the embryo). It mediates nidation of the egg (via binding of trophoblast L-selectin to carbohydrate receptors of the endometrium, trophoblast integrins, laminin and fibronectin of the endometrial intercellular mass), then proliferates and differentiates into two layers:
 * the inner layer: cytotrophoblast;
 * outer layer: syncytiotrophoblast.

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