Embryonic Stem Cells (ES Cells):
Embryonic stem cells are pluripotent stem cells derived from the inner cell mass
of a blastocyst, an early-stage 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
fertilized human embryo, which raises ethical issues. Those issues include
whether or not a human life at the embryonic stage should be granted the moral
status of a human being.
Embryonic stem cells are distinguished by two distinctive properties:
Their ability to replicate indefinitely
ES cells are pluripotent, that is, they are able to differentiate into all derivatives
of the three primary germ layers: ectoderm, endoderm, and mesoderm. These
include each of the more than 220 cell types in the adult body. Pluripotency
distinguishes embryonic stem cells from adult stem cells found in adults; while
embryonic stem cells can generate all cell types in the body, adult stem cells are
multipotent and can produce only a limited number of cell types.
Additionally, under defined conditions, embryonic stem cells are capable of
propagating themselves indefinitely. This allows embryonic stem cells to be
employed as useful tools for both research and regenerative medicine, because
they can produce limitless numbers of themselves for continued research or