Here's why:
* Fertilization: When a sperm and egg fuse, a single-celled zygote is formed.
* Cleavage: The zygote undergoes rapid cell divisions called cleavage, forming a ball of cells called a morula.
* Blastocyst Formation: The morula continues to divide and develops a fluid-filled cavity, becoming a blastocyst.
The blastocyst is a hollow ball of cells with two distinct cell types:
* Inner cell mass (ICM): These cells are pluripotent stem cells, meaning they can differentiate into any type of cell in the body. This is the origin of the embryo itself.
* Trophoblast: These cells will form the placenta and other structures that support the developing embryo.
So, while the blastocyst contains stem cells, it's not just the mass of stem cells. It's a complex structure with both stem cells and other cells that will play important roles in the development of the embryo.
