Transcript Embryonic Stem Cells

Embryonic Stem Cells
and
Embryology
What are embryonic stem cells?
 derived from embryos
that develop from eggs
that have been fertilized
in vitro
 not derived from eggs
fertilized in a woman's
body
 typically four or five days
old and are a hollow
microscopic ball of cells
called the blastocyst.
 do not have a specific gene code to be an exact
cell
 have all of the genes that the other cells do, but
their genes are activated for a primary purpose of
mitosis without a specialized tissue function
 have not undergone differentiation
 daughter cells derived from these stem cells are
capable of differentiating into almost any kind of
cell
 in the laboratory, stem cells can be manipulated to
take on characteristics of specific cells, such as
heart cells, nerve cells or even pancreatic cells ( a
process called directed differentiation).
 during this process, scientists activate certain
genes, and deactivate other genes.
 as a result, the newly coded cells develop specific
structures to perform certain functions.
Adult Stem Cells
 Stem cells can also
come from any body
cell
 Do not have to be
embryonic
 Cells are already
differentiated
Embryonic Development
 Cleavage: division of cells in the early embryo
 Zygotes of many species undergo rapid cell cycles with no significant
growth, producing a cluster of cells the same size as the original zygote.
 The different cells derived from cleavage are called blastomeres and
form a compact mass called the morula
 Cleavage ends with the formation of the blastula (hollow ball of single
layer of cells)
Early Embryological Development
Week 1
 Following fertilization, the major events of the first week of
development are cleavage, formation of the blastocyst, and
the beginning of the implantation process.
 Blastula is formed
Week 2
 By the end of the second week, the blastocyst
has completed implantation
Week 3
 Gastrulation occurs (bilaminar embryo trilaminar embryo)
- one side of blastula pushes inward
- three cell lineages that will eventually form every system
ectoderm, mesoderm, and endoderm
 This is the time of early tissue and organ differentiation of the
nervous and cardiovascular systems, as well as the formation of
future body cavities.
Embryonic Differentiation
 Ectoderm
nervous system, skin
 Mesoderm
muscles, circulatory,
skeletal, excretory, and
reproductive systems
 Endoderm
linings of digestive and
respiratory tracts, liver,
pancreas
Week 4

In week 4, the embryo undergoes major
morphological changes as it changes from a
trilaminar disk-shaped embryo to a cylindrical
embryo.

This is also an important week in terms of
determining placement of future organs.

Following median and horizontal folding, many
organs and body cavities will begin to form or will be
repositioned.