How do repeated cell divisions transform a zygote into a blastocyst?

The transformation of a zygote into a blastocyst occurs through a series of rapid cellular divisions known as cleavage. During this phase, the zygote undergoes mitosis to produce smaller cells called blastomeres. Because there is little growth between these divisions, the total mass of the organism remains roughly the same as the original zygote.12

As these divisions continue, the cells form a solid, berrylike cluster called a morula. Once the morula reaches approximately 30 or more cells, fluid begins to accumulate between the internal cells. These fluid-filled spaces eventually coalesce into a single, subcentral cavity known as the blastocoel.134

This process results in the formation of the blastocyst, which is characterized by two distinct cell types:
* Inner cell mass: An eccentric cluster of cells that will develop into the embryo.14
* Trophoblast: An enveloping outer layer of cells that will contribute to the formation of the placenta and fetal membranes.14