Stem cell, coloured scanning electron micrograph (SEM). Stem cells can differentiate into any other cell type. There are three main types of mammalian stem cell: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in some adult tissues; and cord blood stem cells, which are found in the umbilical cord. The type of cell they mature into depends upon the biochemical signals received by the immature cells.
