What is the part of the uterine lining that develops into the maternal portion of the placenta after interacting with the blastocyst?

The correct answer focuses on the decidua basalis, which is the specific region of the uterine lining that interacts with the developing blastocyst during early pregnancy. After implantation of the embryo into the uterine wall, the decidua basalis forms the maternal portion of the placenta. This area is essential because it provides the necessary support and nutrients for the growing embryo and facilitates the exchange of gases and waste products between maternal and fetal blood.

The decidua capsularis is a different part of the uterine lining that envelops the implanted embryo but does not contribute to the maternal portion of the placenta. The decidua parietalis, also known as the decidua reflexa, refers to the part of the uterine lining that is not directly involved in placental formation. Decidua vera is an older term that generally encompasses the entire decidual tissue but is not specific to the formation of the placenta.

Understanding the role of the decidua basalis is crucial in recognizing how the placenta develops and functions, making it the correct answer in the context of this question.