Stem Cells Introduction
(A) gut, (B) neural cells, (C) bone marrow cells, (D)
cartilage, (E) muscle and (F) kidney cells.
A stem cell is an unspecialized cell that gives rise
to a specific specialized cell, such as a blood cell.
They have the ability to divide for indefinite periods
in culture and to give rise to specialized cells.
They are best described in the context of normal human
development. Human development begins when a sperm fertilizes
an egg and creates a single cell that has the potential
to form an entire organism. This fertilized egg is totipotent,
meaning that its potential is total.
This cell begins
to divide immediately. Approximately four days after
fertilization and after several cycles of cell division,
these totipotent cells begin to specialize, forming
a hollow sphere of cells, called a blastocyst.
The blastocyst
has an outer layer of cells. Inside the hollow sphere,
there is a cluster of cells called the inner cell mass.
The inner cell mass cells will go on to form virtually
all of the tissues of the human body. Although the inner
cell mass cells can form virtually every type of cell
found in the human body, they cannot form an organism.
These inner cell mass cells are pluripotent —
they can give rise to many types of cells but not all
types of cells necessary for fetal development.
The pluripotent stem cells undergo further specialization
into stem cells that are committed to give rise to cells
that have a particular function. These more specialized
stem cells are called multipotent.
While stem cells are extraordinarily important in early
human development, multipotent stem cells are
also found in children and adults.
Adapted from: http://www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html
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