Trophoblast

Common card · No. 438543

The trophoblast (from Greek trephein: to feed; and blastos: germinator) derives from the trophectoderm, the outer layer of epithelial cells of the blastocyst. The trophectoderm is a temporary layer of cells. At the beginning of implantation, on attachment to the endometrium, the cells undergo the process of epithelial–mesenchymal transition allowing invasion of the embryo. The cells are then known as the trophoblast, needed for the formation of much of the placenta. Trophoblasts are present four days after fertilization in humans. As part of the placenta they provide nutrients to the embryo. They form during implantation, the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures that do not directly contribute to the embryo. In the blastocyst the trophoblast is contiguous with the ectoderm of the embryo and is referred to as the trophectoderm. After the first differentiation, the cells in the human embryo lose...

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