sources of stem cells in the human body
there are two broad types of stem cells : embryonic stem cells , which are isolated from the inner cell mass of blastocysts , and adult stem cells , which are found in various tissues . In adult organisms , stem cells and progenitor cells act as a repair system for the body , replenishing adult tissues . In a developing embryo , stem cells can differentiate into all the specialized cells -- ectoderm , endoderm and mesoderm ( see induced pluripotent stem cells ) -- but also maintain the normal turnover of regenerative organs , such as blood , skin , or intestinal tissues .