Begins with the fertilization of an egg by a sperm. A fertilized egg is called a zygote.
The fertilized egg divides into two cells and then into four cells. These are embryos at the 2-cell and 4-cell stage.
The embryo will continue to divide until it forms a solid
ball of 64 cells called a morula. Human embryology is
just like the embryology of all other animals until the
morula stage. Cells in the morula stage are totipotent
What is a stem cell?
· A cell in the body whose job has not yet been
What is meant by totipotent?
· a cell with the “total” potential to develop into
a new individual. They can become ANY cell
in the body.
The morula will then hollow out forming a blastula.
Four days after fertilization, hatching occurs. The
blastula emerges from the hardened zona pellicida (ZP).
Four to six days after fertilization, cells within the
Blastula will become differentiated into two types of
cells, embryonic stem cells and trophoblasts. The
inner cell mass (ICM) contains the 40 embryonic stem
cells that will become the fetus and amniotic sac. The trophoblasts will become the placenta.
· These cells of the blastula are pluripotent.
What is meant by pluripotent?
· a cell with the “most” potential to develop into
different cells. They can become ALMOST ANY
cell in the body.
Pluripotent stem cells in the ICM will differentiate into
4 major branches.
1. HSC – Hematopoetic Stem Cells
(all blood cells)
2. MSC – Mesenchymal Stem Cells
Tendon cells Muscle cells
Adipose cells Marrow cells
3. ESC – Endodermal Stem Cells
(digestive tract & lungs)
4. NSC – Neural Stem Cells
(brain and nerve cells)
Glial cells Astrocytes
· These four major branches will differentiate into
210 types of specialized somatic (body) cells.
Stem cells from the placenta and adult stem cells are multipotent.
What is meant by multipotent?
· a cell with “much” potential to develop into
different cells. They can become A LIMITED
RANGE of cells in the body.