<P> Embryonic stem cells (ES cells or ESCs) are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early - stage pre-implantation embryo . Human embryos reach the blastocyst stage 4--5 days post fertilization, at which time they consist of 50--150 cells . Isolating the embryoblast, or inner cell mass (ICM) results in destruction of the blastocyst, a process which raises ethical issues, including whether or not embryos at the pre-implantation stage should have the same moral considerations as embryos in the post-implantation stage of development . Researchers are currently focusing heavily on the therapeutic potential of embryonic stem cells, with clinical use being the goal for many labs . Potential uses include the treatment of diabetes and heart disease . The cells are being studied to be used as clinical therapies, models of genetic disorders, and cellular / DNA repair . However, adverse effects in the research and clinical processes such as tumours and unwanted immune responses have also been reported . </P> <P> Embryonic stem cells (ESCs), derived from the blastocyst stage of early mammalian embryos, are distinguished by their ability to differentiate into any cell type and by their ability to propagate . It is these traits that makes them valuable in the scientific / medical fields . ESC are also described as having a normal karyotype, maintaining high telomerase activity, and exhibiting remarkable long - term proliferative potential . </P>

What is the origin of es cells in development