Figure 2.

Schematic representation of blastocyst adhesion to the endometrial epithelium and subsequent trophoblast invasion into the endometrium. The developing blastocyst—consisting of the fluid-filled blastocoel, the embryoblast encompassing the inner cell mass, and the outer trophoblast cell layer—adheres to the uterine surface epithelium. Adhesion induces processes in both the embryonic blastocyst and the maternal epithelial and stromal cell layers, which result in the transmigration of the trophoblast through the epithelial layer and the invasion of the endometrial stromal compartment. Subsequently, specialized single trophoblast cells, the extravillous trophoblasts, invade the decidua and erode endothelia and glandular epithelia from their respective basal sides. For further details, see Info Box 3 (Appendix A).