Trophoblast

The outer cell layer of a mammalian blastocyst. It mediates implantation in the uterine wall and contributes fetal tissues to the placenta.

Blastocyst: An early mammalian embryo consisting of an inner cell mass, a fluid-filled cavity, and an outer cell layer. The trophoblast is the blastocyst’s outer layer.
Inner cell mass: The cluster of cells inside the blastocyst that gives rise to the embryo proper and some extraembryonic tissues. Unlike the trophoblast, it forms the embryo proper.
Placenta: A temporary organ that exchanges gases, nutrients, and waste between a pregnant parent and fetus. Trophoblast forms the fetal component of this exchange organ.
Mammalian embryogenesis: The sequence of developmental events through which a mammalian embryo forms and begins to organize its tissues. Trophoblast emerges during the early stages of this developmental sequence.
Blastocyst implantation: The process by which a blastocyst attaches to and embeds in the uterine lining. Trophoblast cells initiate attachment and mediate invasion into the uterine lining.
Trophectoderm: The outer epithelial cell layer of the preimplantation mammalian embryo, which gives rise to trophoblast. It is the developmental precursor of trophoblast in mammals.
Placental villi: Branching projections of fetal placental tissue that increase the surface area for maternal–fetal exchange. Trophoblast covers the villi and helps form their exchange surface.
Morula: A compact ball of cells formed by cleavage divisions before the mammalian embryo develops a blastocyst cavity. The embryo’s outer cells become trophectoderm as it progresses beyond this stage.
Syncytiotrophoblast: A multinucleated outer placental layer formed when trophoblast cells fuse. This invasive layer develops from trophoblast and contacts maternal blood.
Uterine endometrium: The mucosal lining of the uterus, which changes during the menstrual cycle and supports implantation. It is the maternal tissue contacted and invaded during implantation.

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