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How does the placenta form from fetal and maternal tissues?

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The placenta is a vital organ formed through the interaction of fetal and maternal tissues, enabling the exchange of nutrients, gases, and waste between the mother and the developing fetus.12

Fetal Component

The fetal portion of the placenta originates from the trophoblast, a layer of cells on the surface of the blastocyst. Following implantation, the trophoblast invades the uterine lining and develops into chorionic villi—treelike, branching structures that contain fetal blood vessels. These villi eventually form the chorion frondosum, which constitutes the fetal side of the mature placenta.13

Maternal Component

The maternal component, known as the decidua basalis, is derived from the endometrium (the uterine lining) that is in direct contact with the invading conceptus. As the trophoblast erodes maternal tissue, it creates intervillous spaces that fill with maternal blood from uterine arteries.13

Interaction

The fetal villi are bathed in this maternal blood, creating a "placental barrier" that allows for the diffusive exchange of substances without the direct mixing of maternal and fetal bloodstreams.324