الفهرس 
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Abstract
Stem cells are undifferentiated biological cells that can differentiate into
specialized cells and can divide (through mitosis) to produce more stem cells.
They are found in multicellular organisms. In mammals, there are two broad
types of stem cells: embryonic stem cells, which are isolated from the inner cell
mass of blastocysts, and adult stem cells, which are found in various tissues.
Properties of stem cells:
Self-renewal: the ability to go through numerous cycles of cell
division while maintaining the undifferentiated state.
Potency: the capacity to differentiate into specialized cell types. In the
strictest sense, this requires stem cells to be either totipotent or pluripotent—
to be able to give rise to any mature cell type, although multipotent or
unipotent progenitor cells are sometimes referred to as stem cells. Apart
from this it is said that stem cell function is regulated in a feed back
mechanism.
Types of stem cells:-
Not all stem cells come from an early embryo. In fact, we have stem cells in
our bodies all our lives. One way to think about stem cells is to divide them into
three categories:
1. Embryonic stem cells: grown in the laboratory from cells found in the
early embryo
2. Tissue stem cells: found in our bodies all our lives
3. Induced pluripotent stem cells, or „reprogrammed‟ stem cells: similar to
embryonic stem cells but made from adult specialised cells using a
laboratory technique discovered in 2006
Stem cell plasticity:
Stem cell plasticity refers to the ability of some stem cells to give rise to
cell types, formerly considered outside their normal repertoire of differentiation
for the location where they are found. Included under this umbrella title is often
the process of “transdifferentiation”
Most adult tissues have multipotential stem cells (Adult stem cells), cells
capable of producing a limited range of differentiated cell lineages appropriate
to their location, for example, small intestinal stem cells can produce all four
indigenous lineages (lysozyme-secreting Paneth cells, mucin-producing goblet
cells, absorptive columnar cells, and enteroendocrine cells). However, tissuebased
stem cells may be more versatile than previously thought, particularly
those of bone marrow, and these cells may generate unexpected cell types when
engrafted in a damaged non-hematopoietic tissue or organ. This so-called
plasticity is being exploited in the field of regenerative medicine where it is
hoped to produce new cell therapies for currently intractable diseases such as
diabetes and congestive heart failure. Other sources of malleable stem cells
include umbilical cord, blood, mesenchymal stem cells(MSCs) from many
sources including liposuction waste (fat), skin fibroblasts, and spermatogonia.