The blastocyst consists of an outer layer and an inner cell mass. What is the name of the outer layer?

The blastocyst consists of an outer layer and an inner cell mass. What is the name of the outer layer?

• A. Inner cell mass
• B. Yolk sac
• C. Chorion
• D. Trophoblast

Answer: (D)

The outer layer of the blastocyst is the trophoblast. This layer surrounds the inner cell mass, which becomes the embryo (embryoblast). The trophoblast will differentiate and work with maternal tissue to form the placenta and chorionic structures, enabling nutrient exchange between mother and developing fetus. The inner cell mass is the source of the embryo itself, the yolk sac is an early nutritive structure, and the chorion is the outer fetal membrane formed from the trophoblast and extraembryonic mesoderm—distinct from the initial outer layer of the blastocyst.

The outer layer of the blastocyst is the trophoblast. This layer surrounds the inner cell mass, which becomes the embryo (embryoblast). The trophoblast will differentiate and work with maternal tissue to form the placenta and chorionic structures, enabling nutrient exchange between mother and developing fetus. The inner cell mass is the source of the embryo itself, the yolk sac is an early nutritive structure, and the chorion is the outer fetal membrane formed from the trophoblast and extraembryonic mesoderm—distinct from the initial outer layer of the blastocyst.