Stem Cells

Introduction

Stem cells are the mother or master cells of the body which have the property to divide and differentiate into different specialized as well as non-specializing cell types. They have the incredible potential of developing into all types of specialized tissues and organs during the early stage of life and growth while in the later stage of life; they play a major role in renewal and repairing of different tissues and cells. When the stem cells divide, they either remain the stem cells itself or differentiate into specialized cells.

In adults, the stem cells present in bone marrow and gut always divide and differentiate to replace the damaged and worn out tissues while the stem cells present in other organs like heart, pancreas etc. divide only in some special circumstances.

Properties of Stem cells

All the stem cells have the following properties which do not depend on their source:

1.      They are non-specializing cells: Stem cells do not have any kind of tissue related structures which would help them to perform any tissue specific task. E.g. When present in heart, they cannot help in pumping of blood.

2.      They can divide and proliferate for long period of time: Unlike other cells which divide for only a particular number of times, the stem cells can divide for long period of time either into specialized or non-specializing kind of cells. So they have the capability of producing new cells as well as to self renew their own population.

3.      They can differentiate into specialized cells: When the stem cells divide and develop into any specialized type of cell, it is known as differentiation. The micro-environment of the cell i.e. the neighboring tissues and chemical secretions, effect the specialization of the stem cells. They directly or indirectly affect the coding of the DNA and expression of different kind of genes which results in the development of tissue specific mechanism of the cell.

Potency of stem cells

The differentiating capacity of different kinds of stem cells is known as potency. Following types of potency are present in the stem cells:

a)      Totipotent: Some stem cells have the capacity to divide into all types of specialized tissues; they can even give rise to a complete organism. These kinds of stem cell arise by the fusion of gametes, i.e. sperm and ovum. They are found in human embryo at the early stage of development (initial weeks).

b)      Pluripotent: These cells are found in the later stages of embryonic development. They have the capacity of developing into nearly all cell types i.e. nerve cells, liver cells, kidney cells etc.

c)      Multipotent: These stem cells have the capability of differentiating into only the closely associated family of cells.

Sources of Stem cells

Majorly there are three sources of stem cells:

1.      Embryonic Stem Cells: The stem cells which are derived from the early stage of embryonic development are known as embryonic stem cells. They are the totipotent cells which have the capability of developing into a whole organism.

2.      Foetal Stem cells: these stem cells are found in the organs of foetus as well as in the amniotic fluid and cord blood. They are the pluripotent stem cells which can differentiate into nearly all types of specialized cells.

3.      Adult Stem Cells: The Adult stem cells are majorly multipotent but there are evidences that pluripotent stem cells also exists in adults. The major source of adult stem cells is the bone marrow.