Blastocyst is one of the stages of embryonic development. It contains several dozens of cells, among which the distinct cell population occurs — inner cell mass or embryoblast. The embryoblast gives rise to all embryonic tissues and some non-embryonic organs (yolk sac, allantois and amnion).
The blastocyst, when it is not implanted into the uterus tissue, is the particular stage to isolate embryonic stem cells. These cells have unique features – they proliferate and can maintain the undifferentiated state in vitro, besides, they have the potential to differentiate into all cell types of the body.
Cells of an adult are on different stages of their development. There are some tissue types that renew their cell population constantly (blood, epithelium and others). The integrity of such tissues is maintained by a special cell type – adult stem cells.
Adult stem cells are the undifferentiated cell population that restores the tissues' and organs' cell compound. Every tissue type has its own stem cells (hemopoietic stem cells, neural stem cells, muscle stem cells, epidermal stem cells and others) that repair and regenerate it. Adult stem cells have limited differentiation potential in comparison with embryonic stem cells. The number of adult stem cells is limited, and normally they are in dormant state. Their activation occurs in case of organ injure, for example.