Question

Cytotrophoblast invades which structure?

• A. Decidua parietalis
• B. Decidua basalis
• C. Decidua capsularis
• D. None

Hint:

Cytotrophoblast columns pass through the syncytiotrophoblast to reach the decidua basalis under the embryo.

Answer 1

The Correct Option is B

Step 1: After the blastocyst embeds in the endometrial stroma, the trophoblast differentiates into two layers - an inner cytotrophoblast and an outer syncytiotrophoblast.

Step 2: The syncytiotrophoblast is the invasive outer layer that erodes the uterine epithelial cells and maternal tissue first. The cytotrophoblast then proliferates and pushes through the overlying syncytiotrophoblast to invade the decidua basalis.

Step 3: The decidua basalis is the part of the decidua deep to the implanted conceptus and forms the maternal part of the placenta, so it is the layer the cytotrophoblast invades.

Step 4: Why the others are wrong - the decidua capsularis overlies the conceptus toward the uterine cavity and the decidua parietalis lines the rest of the uterine cavity; neither is the primary site of cytotrophoblast invasion. Hence decidua basalis is correct.