Embryonic stem cell
Human embryonic stem cells in cell culture
Pluripotent, embryonic stem cells originate
as inner mass cells within a blastocyst. The
stem cells can become any tissue in the body,
excluding a placenta. Only the morula’s cells
are totipotent, able to become all tissues and
a placenta.
Embryonic stem cells (ES cells) are stem
cells derived from the inner cell mass of an
early stage embryo known as a blastocyst.
Human embryos reach the blastocyst stage
4–5 days post fertilization, at which time they
consist of 50–150 cells.
Embryonic Stem (ES) cells are pluripo-
tent. This means they are able to differenti-
ate into all derivatives of the three primary
germ layers: ectoderm, endoderm, and meso-
derm. These include each of the more than
220 cell types in the adult body. Pluripotency
distinguishes ES cells from multipotent pro-
genitor cells found in the adult; these only
form a limited number of cell types. When
given no stimuli for differentiation, (i.e. when
grown in vitro), ES cells maintain pluripo-
tency through multiple cell divisions. The
presence of pluripotent adult stem cells re-
mains a subject of scientific debate; however,
research has demonstrated that pluripotent
stem cells can be directly generated from
adult fibroblast cultures.[1]
Because of their plasticity and potentially
unlimited capacity for self-renewal, ES cell
therapies have been proposed for regenerat-
ive medicine and tissue replacement after in-
jury or disease. However, to date, no ap-
proved medical treatments have been derived
from embryonic stem cell research. Adult
stem cells and cord blood stems cells have
thus far been the only stem cells used to suc-
cessfully treat any diseases. Diseases treated
by these non-embryonic stem cells include a
number of blood and immune-system related
genetic diseases, cancers, and disorders; ju-
venile diabetes; Parkinson’s; blindness and
spinal cord injuries. Besides the ethical con-
cerns of stem cell therapy (see stem cell con-
troversy), there is a technical problem of
graft-ver