such as "Introduction", "Conclusion"..etc
The formation of floating and anchoring villi begins immediately
after nidation. Three stages are recognized in the development of the
villi, namely primary, secondary and tertiary villi, the last being
characterized by a de-novo formation of capillaries from mesenchymal
precursors and thus devoted to feto-maternal exchanges. Villous tree
expansion occurs throughtout pregnancy .
The specialized villous cell types, i.e. ST and extravillous
trophoblast (EVT) cells, originate from cytotrophoblast (CT) stem
cells. During blastocyst implantation, CT cells fuse to form an
external layer of non-proliferative multinucleated ST which then grows
thanks to the steady incorporation of new CT cells. ST exerts a crucial
role in feto-maternal exchanges and possesses endocrine activity,
releasing hormones involved in the homeostasis of pregnancy such as
chorionic gonadotrophin (CG) and placental lactogen (PL). Around day 14
after implantation, CT cells break through the ST layer giving rise to
EVT cells, which begin to invade the uterine stroma as trophoblastic
cell columns. From the tips of the columns, a subpopulation of these
motile and invasive cells moves laterally, to form the trophoblastic
shell, and longitudinally to invade deeply the decidua and the deeper
portion of the myometrium, where these cells evoke profound changes
within the uterine vessels .
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