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The formation of syncytiotrophoblast from cytotrophoblast is a terminal differentiation step of trophoblastic cells. [2] Syncytialization of cytotrophoblastic cells can be induced in vitro through multiple signalling molecules including epidermal growth factor, glucocorticoids, and human chorionic gonadotropin. [3] [4] [5]
This core is surrounded by two layers of trophoblasts, the cytotrophoblast and the syncytiotrophoblast. The cytotrophoblast is a layer of mono-nucleated cells that resides underneath the syncytiotrophoblast. [6] The syncytiotrophoblast is composed of fused cytotrophoblasts which then form a layer that covers the placental surface. [6]
A cytotrophoblast cap penetrates through the fetus' syncytiotrophoblasts and reaches the maternal decidua, forming the anchoring villus. [1] [3] [4] The cytotrophoblast layer spreads and contacts the cytotrophoblast layers of neighboring anchoring villi, creating a continuous layer called the cytotrophoblastic shell.
Before gastrulation, the cells of the trophoblast become differentiated into two layers: The outer layer forms a syncytium (i.e., a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells), termed the syncytiotrophoblast, while the inner layer, the cytotrophoblast, consists of well-defined cells.
Image showing trophoblast differentiated into the two layers of cytotrophoblast and syncytiotrophoblast during implantation. It is the outer layer of the trophoblasts and actively invades the uterine wall, during implantation, rupturing maternal capillaries and thus establishing an interface between maternal blood and embryonic extracellular fluid, facilitating passive exchange of material ...
In the placenta, the intervillous space is the space between chorionic villi, and contains maternal blood.. The trophoblast, which is a collection of cells that invades the maternal endometrium to gain access to nutrition for the fetus, proliferates rapidly and forms a network of branching processes which cover the entire embryo and invade and destroy the maternal tissues.
The blastocyst has a diameter of about 0.1–0.2 mm and comprises 100-200 cells following 7-8 rounds of cleavage (cell division without cell growth). About seven days after fertilization, [ 6 ] the blastocyst undergoes implantation , embedding into the endometrium of the uterine wall where it will undergo further developmental processes ...
Fluid collects between the epiblast and the hypoblast, which splits the epiblast into two portions. The layer at the embryonic pole grows around the amniotic sac, creating a barrier from the cytotrophoblast. This becomes known as the amnion, which is one of the four fetal membranes and the cells it comprises are referred to as amnioblasts. [6]