The placenta forms from which combination of structures?

The placenta forms from which combination of structures?

• A. Chorionic villi and decidua basalis
• B. Amnion and chorion
• C. Yolk sac and placental stalk
• D. Trophoblast and decidua parietalis

Answer: (A)

Placenta formation occurs at the interface where fetal tissue and maternal tissue come together: the chorionic villi from the fetal side invade and interact with the maternal decidua basalis. This combination—chorionic villi plus decidua basalis—forms the placental tissue that supports nutrient and gas exchange between mother and fetus. The amnion and chorion create membranes around the fetus, not the placenta; the yolk sac and placental stalk are embryonic structures associated with early development but not the placental tissue itself; and the decidua parietalis lines the uterus but does not participate in forming the placental interface.

Placenta formation occurs at the interface where fetal tissue and maternal tissue come together: the chorionic villi from the fetal side invade and interact with the maternal decidua basalis. This combination—chorionic villi plus decidua basalis—forms the placental tissue that supports nutrient and gas exchange between mother and fetus. The amnion and chorion create membranes around the fetus, not the placenta; the yolk sac and placental stalk are embryonic structures associated with early development but not the placental tissue itself; and the decidua parietalis lines the uterus but does not participate in forming the placental interface.