Unformatted text preview: Stem Cells Diversity of Human Cells
Adult humans consist of more than 200
kinds of cells.
They are nerve cells (neurons), muscle cells
(myocytes), skin (epithelial) cells, blood
cells (erythrocytes, monocytes,
lymphocytes, etc.), bone cells (osteocytes),
and cartilage cells (chondrocytes).
cells essential for embryonic development
but not incorporated into the body of the
embryo, include the extra-embryonic
tissues, placenta, and umbilical cord.
All of these cells are generated from a
single, totipotent cell, the zygote, or
fertilized egg. What is a stem cell? A stem cell is a "blank" cell/ precursor cell that can give rise
to multiple tissue types such as
a skin, muscle, or nerve cell. A stem cell is essentially the
building block of the human
4. 5. Features of Stem
Cells are very unique cells.
Stem Cells have the amazing ability to develop
into several distinct cell types in the body.
Stem Cells can be used as a repair system for
Stem Cells can theoretically divide without
limit in a living organism in order to replenish
various types of cells.
When a stem cell divides, each new cell has the
potential to either remain a stem cell or
become another type of cell with a more
specialized function (i.e. a muscle cell, a red
blood cell, a brain cell, etc.). Three unique properties of
Stem cells are capable of dividing
and renewing themselves for long
They are “unspecialized” and they
can give rise to specialized cell
A stem cell is "uncommitted," until
it receives a signal to develop into a
specialized cell. Asymmetric division of
Stem cells have the ability
to divide asymmetrically .
One portion of the cell
division becomes a
differentiated cell while
the other becomes another
stem cell. 1. Stem cells are
unspecialized A stem cell does not have any
tissue-specific structures that allow
it to perform specialized functions.
A stem cell cannot work with its
neighbors to pump blood through
the body (like a heart muscle cell);
It cannot carry molecules of oxygen
through the bloodstream (like a red
blood cell); and
It cannot fire electrochemical
signals to other cells that allow the
body to move (like a nerve cell). 2.Stem cells are capable of dividing and renewing
themselves for long periods.
Stem cells may replicate many
When cells replicate themselves
many times it is called proliferation.
The stem cells that proliferate for
many months in the laboratory can
yield millions of cells.
Stem cells are capable of long-term
self-renewal. 3.Stem cells can give rise
to specialized cells When unspecialized stem cells give rise to
specialized cells, the process is called
There are signals inside and outside cells
that trigger stem cell differentiation.
The internal signals are controlled by a
The external signals include chemicals
secreted by other cells, physical contact
with neighboring cells, and certain
molecules in the microenvironment 4.Stem cells exist in both
embryos and adults.
In embryos, stem cells
function to generate new
organs and tissues.
In adults, they function to
replace cells during the
natural course of cell
turnover. Distinguishing Features of
Progenitor/Precursor Cells and
Stem Cells. A stem cell is an unspecialized cell that
develops into a variety of specialized cell
a stem cell divides and gives rise to one
additional stem cell and a specialized cell.
Example: a hematopoietic stem cell produce a
second generation stem cell and a neuron.
A progenitor cell (a precursor cell) is
unspecialized that is capable of undergoing
cell division and yielding two specialized cells.
Example: a myeloid progenitor/precursor cell
undergoing cell division to yield two
specialized cells (a neutrophil and a red blood
cell). Stem cell
Classes Embryonic Type stem
1.Embryonic Type Embryonic Germ Cel
Embryonic Stem Cells Adult type Stem cells
2. Adult Type Umbilical Cord Stem Cells Placental Stem Cells Adult Stem Cells Sources of embryonic
type stem cells * Embryos - Embryonic stem cells are obtained by harvesting living embryos
which are generally 5-7 days old. The
removal of embryonic stem cells
invariably results in the destruction of
* Fetuses - Another kind of stem cell,
called an embryonic germ cell, can be
obtained from either miscarriages or
aborted fetuses. Sources of adult type
stem cells Umbilical Cords, Placentas and Amniotic
Fluid - Adult type stem cells can be derived
from various pregnancy-related tissues.
Adult Tissues - In adults, stem cells are
present within the bone marrow, liver,
epidermis, retina, skeletal muscle,
intestine, brain, dental pulp and
Cadavers - Neural stem cells have been
removed from specific areas in postmortem human brains as late as 20 hours
following death. Comparison of
stem cells Advantages of Embryonic Stem Cell 1. Flexible - appear to have the potential
to make any cell. 2. Immortal - one embryonic stem cell
line can potentially provide an endless
supply of cells with defined
characteristics. 3. Availability - embryos from in vitro
fertilization clinics. Disadvantages of
1. Difficult to differentiate uniformly and
homogeneously into a target tissue.
2. Immunogenic - embryonic stem cells
from a random embryo donor are likely
to be rejected after transplantation
3. Tumorigenic - capable of forming
tumors or promoting tumor formation.
4. Destruction of developing human life. Advantages of Adult Stem
Cell 1. Adult stem cells from bone marrow and
umbilical cords appear to be as flexible as
the embryonic type
2. Somewhat specialized - inducement may be
3. Not immunogenic - recipients who receive
the products of their own stem cells will
not experience immune rejection.
4. Relative ease of procurement - some adult
stem cells are easy to harvest (skin,
muscle, marrow, fat)
5. Non-tumorigenic-tend not to form tumors.
6. No harm done to the donor. Disadvantages of Adult
stem cells 1. Limited quantity - can sometimes be difficult to obtain
in large numbers. 2. Finite - may not live as long
as embryonic stem cells in
culture. 3. Less flexible - may be more
difficult to reprogram to form
other tissue types Why are adult stem cells
preferable to embryonic stem
cells? Adult stem cells are naturally exist in
our bodies, and they provide a natural
repair mechanism for many tissues.
They belong in the microenvironment
of an adult body, while embryonic
stem cells belong in the
microenvironment of the early
embryo, where they tend to cause
tumors and immune system reactions. Superior features of
ESCs Embryonic stem cells are easier to
identify, isolate and harvest.
There are more of them.
They grow more quickly and easily
in the lab than adult stem cells.
They can be more easily
manipulated (they are more
plastic) Classification based
on level of
Unipotent stem cells Types
cells Totipotent stem cells
1. 2. 3. The fertilized egg is said to be
totipotent from the Latin totus,
It has the potential to generate
all the cells and tissues that
make up an embryo.
It supports embryonic
development in utero. Pluripotent stem cells
Pluripotent stem cells are
descendants of the totipotent stem
cells of the embryo.
These cells develop about four
days after fertilization
They can differentiate into any cell
type, except for totipotent stem
cells and the cells of the placenta. Pluripotent stem cells
“Pluri” is derived from the
Latin plures means several or
Thus, pluripotent cells have
the potential to give rise to
any type of cell. Pluripotent stem cells These cells cannot recreate a complete
organism but differentiate
to a large number of
mature tissue types, for
example, brain and
muscle. Multipotent stem
cells Multipotent stem cells are
descendents of pluripotent stem
cells and antecedents of specialized
cells in particular tissues.
For example, hematopoietic stem
cells, which are found primarily in
the bone marrow, give rise to all of
the cells found in the blood,including
red blood cells, white blood cells,
and platelets. Unipotent stem cell
Unipotent stem cell, a term
that is usually applied to a
cell in adult organisms, means
that the cells in question are
capable of differentiating
along only one lineage.
"Uni" is derived from the Latin
word unus, which means one. Progenitor
Progenitor cells (or
unipotent stem cells) can
produce only one cell type.
For example, erythroid
differentiate into only red
blood cells. Blood is made in the Bone
Marrow-Blood Cell Development “Terminally differentiated"
At the end of the long chain
of cell divisions are
cells, such as a liver cell or
lung cell, which are
permanently committed to
specific functions. Adult stem cells
(ASC) Adult stem cells or
somatic stem cells
Adult stem cells are undifferentiated
They are found in small numbers in most
They can also be extracted from
umbilical cord blood.
They are also called “somatic stem cells,”
They are multipotent in nature.
They give rise to a closely related family
of cells within the tissue.
An example is hematopoietic stem cells,
which form all the various cells in the
blood. Adult stem cell
transdifferentiation This ability to
multiple cell types is
called plasticity or
pathways of adult
Neural stem cells in the brain give rise to its Neural stem cells in the brain give rise to its
three major cell types: nerve cells (neurons) and
two categories of non-neuronal cells —
astrocytes and oligodendrocytes.
Epithelial stem cells in the lining of the digestive
tract occur in deep crypts and give rise to
several cell types: absorptive cells, goblet cells,
Paneth cells, and enteroendocrine cells.
Skin stem cells occur in the basal layer of the
epidermis and at the base of hair follicles.
The epidermal stem cells give rise to
keratinocytes, which migrate to the surface of
the skin and form a protective layer.
The follicular stem cells can give rise to both
the hair follicle and to the epidermis The similarities and differences
between embryonic and adult
Embryonic stem cells can become all
cell types of the body because they
Adult stem cells are generally limited
to differentiating into different cell
types of their tissue of origin.
However, some evidence suggests that
adult stem cell plasticity may exist,
increasing the number of cell types a
given adult stem cell can become. Human embryonic and
adult stem cells
A potential advantage of using stem
cells from an adult is that the patient's
own cells could be expanded in culture
and then reintroduced into the patient.
The use of the patient's own adult stem
cells would mean that the cells would
not be rejected by the immune system.
Embryonic stem cells from a donor
introduced into a patient could cause
transplant rejection. Umbilical cord stem
Blood from the placenta and umbilical
cord that are left over after birth is a
rich source of hematopoietic stem cells.
These so-called umbilical cord stem
cells have been shown to be able to
differentiate into bone cells and
neurons, as well as the cells lining the
inside of blood vessels. Importance of
Cord blood stem cells
Cord blood stem cells have been
used to treat 70 different diseases,
including leukemia, lymphoma, and
inherited diseases (of red blood
cells, the immune system, and
certain metabolic abnormalities).
Cord blood collection is a safe,
simple procedure that poses no risk
to the mother or newborn baby. Embryonic Stem Cells
(ESC). Embryonic Stem Cells Embryonic Stem Cells are derived
from embryos that develop from eggs
that have been fertilized in vitro.
Embryonic Stem Cells are never
derived from eggs fertilized inside of a
The embryos from which Human
Embryonic Stem Cells are derived are
typically four or five days old and are
a hollow microscopic ball of cells
called the blastocyst Embryonic stem cells
Embryonic stem cells (ESC), as their name
suggests, are derived from embryos.
Specifically, embryonic stem cells are
derived from embryos that develop from
eggs that have been fertilized in vitro —
donated for research purposes with
informed consent of the donors.
They are not derived from eggs fertilized
in a woman's body. Properties of Embryonic
Stem Cells a Derived from the inner cell mass of the
a Capable of undergoing an unlimited number
of symmetrical divisions without
differentiating (long-term self-renewal).
Exhibit and maintain a stable, full (diploid),
normal complement of chromosomes
Pluripotent ES cells can give rise to
differentiated cell types that are derived from
all three primary germ layers of the embryo
(endoderm, mesoderm, and ectoderm). Potential sources of stem
cells are: fetal tissue that becomes available after an
excess embryos from assisted reproductive
technologies such as commonly used in
embryos created through in vitro fertilization
specifically for research purpose, and
embryos created asexually as a result of the
transfer of a human somatic cell nucleus to an
egg with its own nucleus removed.
Other sources of stem cells are those from
umbilical cord blood, and bone marrow.
In addition, neural stem cells, haematopoetic
stem cells and mesenchymal stem cells can be
harvested from fetal blood and fetal tissue. Cell therapy. Treatment of neural diseases such
as Parkinson's disease, Huntington’s
disease and Alzheimer's disease.
Stem cells could be used to repair or
replace damaged neurons.
Repair of damaged organs such as
the liver and pancreas.
Treatments for AIDS. Stem cell
transplantation (SCT) Stem cell transplantation (SCT) is the
term now used in preference to bone
marrow transplantation (BMT).
When a patient's bone marrow fails to
produce new blood cells, for whatever
reason, he or she will develop anaemia,
be prone to frequent, persistent
infections and may develop serious
In order to restore blood cell production
a patient may be given healthy stem cells. Therapeutic cloning/
somatic cell nuclear
Scientists first remove the nucleus from a
normal egg cell of a woman. They then
extract a nucleus from a somatic cell that is, any body cell other than an egg or
sperm—from a patient who needs an
infusion of stem cells to treat a disease or
injury, and insert the nucleus into the egg.
The egg, which now contains the patient's
genetic material, is allowed to divide and
soon forms a hollow sphere of cells called
Cells from the inner cell mass are isolated
and used to develop new embryonic stem Strategy for therapeutic
cloning and tissue
engineering Stem cells and cancer
Intense chemotherapy damages a person’s bone
marrow, where the stem cells for blood reside.
Depleted of a fresh supply of blood cells, the
patient is left vulnerable to infection, anemia
These side effects of chemotherapy are often
treated with a bone marrow transplant.
“Transplanting bone marrow tissue into a
chemo-cancer patient may involve hundreds of
thousands or millions of cells – of which only two
or three may be actual stem cells.
It would be much more efficient if you could
inject a thousand purified stem cells,” Therapeutic cloning
for tissue repair
One human organ, skin, is readily
cultured to provide replacement
tissue for burns victims.
Healthy skin cells from the
patient can be grown rapidly in
vitro to provide self-compatible
skin grafts. Is Stem Cell Research
Ethical? * Embryonic Stem Cells - always morally
objectionable, because the human embryo must be
destroyed in order to harvest its stem cells. * Embryonic Germ Cells - morally objectionable
when utilizing fetal tissue derived from elective
abortions, but morally acceptable when utilizing
material from spontaneous abortions (miscarriages)
if the parents give informed consent. * Umbilical Cord Stem Cells - morally acceptable,
since the umbilical cord is no longer required once
the delivery has been completed. * Placentally-Derived Stem Cells - morally
acceptable, since the afterbirth is no longer
required after the delivery has been completed. * Adult Stem Cells - morally acceptable. Sources Consulted Odorico, J.S., Kaufman, D.S., and Thomson, J.A.
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(1998). Qualitative and quantitative aspects of
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