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How does the placenta form from maternal and embryonic tissues?

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Fetal growth — human development Growth of the human fetus from the fourth month to the ninth month of pregnancy.

The placenta is a vital organ formed through the interaction of maternal and embryonic tissues to support fetal development. Its formation involves a complex process of implantation and tissue specialization.1234

Embryonic Contribution

The embryonic component originates from the trophoblast, the outer layer of the blastocyst. Upon reaching the uterus, the trophoblast invades the endometrium, forming finger-like projections called chorionic villi. These villi, which contain fetal blood vessels, branch extensively to increase the surface area for nutrient and gas exchange. The fetal portion of the mature placenta is primarily derived from the chorion frondosum.123

Maternal Contribution

The maternal component, known as the decidua basalis, is derived from the modified uterine lining. As the trophoblast invades, it erodes maternal tissues and taps into uterine blood vessels, creating intervillous spaces filled with maternal blood.14

Placental Function

The two circulations remain separate, separated by the placental barrier, which allows for the diffusive exchange of oxygen, nutrients, and waste products between the mother and the fetus.352