Chorion

Chorion is external fetal membrane (due to its appearance it is called "membrane villous"). From the inside, it is formed by extraembryonic mesoderm (subsequently it differentiates into mesenchyme, which then differentiates into fibrous layer), from the outside, it is formed by cytotrophoblast and syncitotrophoblast. It participates in the nutrition of the embryo, it is part of the fetal part of the placenta, villi and trophoblast lacunae. It creates the hormone hCG. From the second month of pregnancy, it is possible to take a sample from the chorion (through the vagina) for examination of the embryo (tissues are identical). During development, the chorion divides into two regions:


 * chorion frondosum − rich in villi, in the region of the embryonic pole, part of the future placenta;
 * chorion leave − it has degenerating villi, abembryonic pole, area outside the placenta.

Related articles

 * Placenta
 * First week of embryo development
 * Portal:Embryonic preparations
 * Prenatal period
 * Amnion
 * Fetal membranes and placenta