How does a morula become a blastocyst?

The transition from a morula to a blastocyst is a key stage in early prenatal development.

A morula is a solid cluster of cells, or blastomeres, formed through the cleavage of a zygote. As the number of cells in the morula increases—typically reaching around 30 or more—the structure transforms into a blastocyst through the following process:

• Fluid Accumulation: Pools of clear fluid begin to accumulate between the internal cells of the morula.1
• Cavity Formation: These individual spaces coalesce to form a single, subcentral cavity known as the blastocoel.1
• Structural Differentiation: The resulting hollow, bubble-like structure organizes into two distinct parts:
  • Inner Cell Mass: An eccentric cluster of cells that will develop into the embryo.12
  • Trophoblast: An external layer of smaller cells that will contribute to the formation of the placenta and fetal membranes.1

Once this hollow structure is formed, the blastocyst eventually sheds its protective gelatinous capsule, the zona pellucida, and prepares for implantation in the uterine lining.12