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What are stem cells? (Everyday Mysteries: Fun Science Facts from the Library of Congress)
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What are stem cells?
Stem cells are the cells that have an ability to
become various types of cells. They are present
both during embryonic development (embryonic
stem cells) and in the adult body (adult stem
cells).
Stem cells have unique properties that other cells do not have. First, to understand what stem cells are, you need to understand
how humans and other mammals develop:
1. Sperm fertilizes an egg and forms a single cell called a
zygote.
'PLURIPOTENT' CELLS — This micrograph
shows a colony of undifferentiated human
embyonic stem cells. Argonne National
Laboratory Web site.
2. The zygote undergoes a process known as mitosis, in
which it replicates its chromosomes (which carry each
parent’s DNA) and then divides, resulting in two identical
cells. These cells are called totipotent and have the ability
to develop into a new organism. The zygote repeats the
process of mitosis for about 5 or 6 days creating a small
ball of a few hundred cells called a blastocyst.
3. The blastocyst has an outer­layer of cells called the
trophoblast, which will eventually form the protective
placenta. Inside the trophoblast is a group of cells called
the inner cell mass. The organism in a stage between
zygote to fetus is called an embryo* and the cells are
called embryonic stem cells.
At this point embryonic stem cells have the ability to
become a cell for any part of the body (nerve, muscle,
blood, etc.). This ability to become any type of cell in the
body is called pluripotent. The difference between
totipotent and pluripotent cells is only that totipotent cells
can give rise to both the placenta and the embryo.
Embryonic stem cells. National Science
Foundation Web site.
4. As the embryo grows these pluripotent cells develop
into specialized, multipotent stem cells. Multipotent stem
cells have the ability to develop specific types of cells
(terminally differentiated cells). For example a blood
stem cell (multipotent) can develop into a red blood cell,
white blood cell or platelets (all specialized cells). There are
multipotent stem cells for all of the different types of tissue
in the body.
https://www.loc.gov/rr/scitech/mysteries/stemcells.html
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What are stem cells? (Everyday Mysteries: Fun Science Facts from the Library of Congress)
*Embryo: the embryo of mammals is defined as the stage
of organism between the first division of zygote and the
time it becomes a fetus through further development. For
humans, the embryo is defined as the implantation of
fertilized egg in the uterus through the eighth week of its
development. The embryo will be called a fetus after the
eighth week until birth.
Stem Cells are different from other cells because:
1. They can continue to divide for long periods of time: Most
cells such as skin cells cannot replicate themselves after a certain
period of time. Stem cells are self­sustaining by replicating
themselves for a much longer period of time.
2. They are unspecialized: Specialized cells have specific
capabilities that allow them to perform certain tasks. For example
a red blood cell contains hemoglobin that allows it to carry
oxygen. Stem cells have unspecialized capability and do not have
tissue­ specific structures to perform specialized functions.
Drawing depicting differentiated cells coming
from embryonic stem cells. National Institutes
of Health, National Institute of General Medical
Sciences Web site.
3. They can give rise to specialized cells: Stem cells go
through a process called differentiation and create special types
of cells (muscle, nerve, skin, etc.).
Embryonic stem cells
Embryonic stem cells are the cells within the protective layer of
the blastocyst. They are pluripotent, which means they can
develop into any of the cells of the adult body. Researchers
believe that, because they are pluripotent, and easy to grow, they
have the best potential for replacing damaged or lost tissue or
body parts.
Adult stem cells
Also known as progenitor cells or somatic stem cells, adult
stem cells are located, in small quantities, throughout the body
and generate specialized cells for the area they are located. These
cells do not renew themselves as well as embryonic stem cells.
Still, if these cells are put in a different environment, they may
produce a different type of cells from the originating cell.
Stem cell research is an active area of inquiry and scientists are
discovering new characteristics of stem cells every day. For
example, recent research indicated that multipotent stem cells
from one type of tissue (blood) might actually have the ability to
generate cells for a different type of tissue (nerve).
Scientists are continuing to search for new sources of adult stem
cells. Some of the locations where stem cells have been located
include: bone marrow, skin, liver, blood, and the brain. Some
adult stem cells, which have already been used to treat illnesses,
include hematopoietic stem cells and umbilical cord blood stem
cells.
Techniques for generating embryonic stem cell
cultures. USDA Center for Biologics
Evaluation and Research Web site.
Hematopoietic stem cells are located in the bone marrow and
form blood cells. They have been successfully used to treat blood
disorders for younger patients. Umbilical cord blood stem cells
are located in the blood of the umbilical cord after birth. Umbilical
cord stem cells are similar to hematopeitetic stem cells in adults,
but they are less mature and have much more potential to
differentiate into various types of cells.
Related Web Sites
International Society for Stem Cell Research­Public
Information ­ This site provides term definitions, answers
to common questions, video clips describing certain
concepts, and more.
https://www.loc.gov/rr/scitech/mysteries/stemcells.html
Biologists Eliezer Huberman (right) and Yong
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What are stem cells? (Everyday Mysteries: Fun Science Facts from the Library of Congress)
National Institutes of Health ­ Stem Cell Information ­ This
site is the stem cell resource for the National Institutes of
Health. It contains detailed information about many
aspects of stem cell research, from basic information to
research, current news and also Federal policies
Nova Science: Stem Cells ­ This site provides information
to commonly asked questions. There are slide shows,
movies, interviews, and an Ask­ the­Expert section.
Zhao discovered that the human blood stream
is a source for stem cells. Argonne National
Laboratory Web site.
Further Reading
Allman, Toney. Stem cells. Detroit, Lucent Books, c2006.
128 p. (Juvenile)
Gibbs, Nancy. Stem cells: the hope and the hype. Time.
v.168, August 7, 2006: 40­46.
Lanza, Robert et al. Essentials of stem cell biology.
Amsterdam, Boston, Elsevier, c2006. 548 p.
Panno, Joseph. Stem cell research: medical applications
and ethical controversy. New York, Facts on File, c2005.
178 p. (Juvenile)
Sohn, Emily. From stem cell to any cell. Science News for
Kids. Oct. 19, 2005.
http://www.sciencenewsforkids.org/articles/20051019
/Feature1.asp For more print resources...
Search on "Stem cells," "Stem Cells physiology" in the
Library of Congress Online Catalog.
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