Practice question

Trophectoderm is outer epithelial layer of blastocyst specified when outer polar cells suppress Hippo kinases, allowing nuclear YAP and induction of Cdx2 transcription factor. This lineage does not contribute to fetus itself but differentiates into cytotrophoblast and syncytiotrophoblast that invade decidua, secrete human chorionic gonadotropin, and build chorionic villi of placenta. It establishes fetomaternal exchange interface providing nutrition, gas exchange, endocrine support and immune protection. Trophoblast commitment therefore underlies implantation, placental development essential for intrauterine fetal survival, growth, maternal adaptation and successful pregnancy maintenance throughout gestation.