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Layer Location Description Cytotrophoblast: The inner layer: A single-celled inner layer of the trophoblast. Syncytiotrophoblast: The outer layer: A thick layer that lacks cell boundaries and grows into the endometrial stroma. It secretes hCG in order to maintain progesterone secretion and sustain a pregnancy. Intermediate trophoblast (IT)
The epiblast gives rise to the three germ layers of the developing embryo during gastrulation (endoderm, mesoderm, and ectoderm). The trophoblast is a layer of cells forming the outer ring of the blastocyst that combines with the maternal endometrium to form the placenta. Trophoblast cells also secrete factors to make the blastocoel. [25]
"Cytotrophoblast" is the name given to both the inner layer of the trophoblast (also called layer of Langhans) or the cells that live there.It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo.
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 ...
The trophoblast then differentiates into an inner layer, the cytotrophoblast, and an outer layer, the syncytiotrophoblast. The cytotrophoblast contains cuboidal epithelial cells and is the source of dividing cells , and the syncytiotrophoblast is a syncytial layer without cell boundaries.
The blastocoel further expands and the inner cell mass becomes positioned on one side of the trophoblast cells forming a mammalian blastula, called a blastocyst. The axis formed by the inner cell mass and the blastocoel is the first axis of symmetry of mammalian embryo and determines its attachment point to the uterus.
As the number of cells grows from 16 to between 40 and 150, the blastocyst differentiates into two layers, an outer sphere of cells called the trophoblast and an inner cell mass called the embryoblast. The spherical outer cell layer (trophoblast), after implantation in the wall of the uterus, further differentiates and grows to form the placenta.
The trophoblast cells form tight junctions between them making the structure leakproof. Trophoblast cells have sodium pumps on their membranes, and pump sodium into the centre of the morula. This draws fluid in through osmosis causing a cavity to form inside the morula, and to increase in size. [ 2 ]