Blastocyst stage embryo

From the fifth day of embryonic development, the embryo takes the form of a blastocyst. The parts that form the blastocyst are as follows:

• Zona pellucida: the membrane that surrounds the embryo and has become thinner as it expands.
• Trophoectoderm: cells that will form the placenta, which are located around the zona pellucida.
• Inner cell mass: cells that will form the future baby.
• Blastocele: internal cavity filled with fluid.