What are Stem Cells

In our body we have a variety of fully differentiated cells, most of them are specific for individual organs. In addition to these mature and fully differentiated cells, there are several populations of cells that keep on constantly regenerating, partly to replenish cells that are lost in regular manner. The replacement cells for these losses come from the cells known as stem cells found in most of the tissues or organs of the body, although some organs like heart and pancreas possess a few or almost no stem cells. Stem cells are known to be present in different parts of an animal’s body and occur along with other specialized cells.These stem cells are characterized by two special attributes. They are able to reproduce themselves throughout the life span of an animal and have the potential to produce at least one type and often several type of specialized cells that make up the body of an individual. A stem cell is thus capable of extensive proliferation, creating more stem cells as well as more differentiated cells.

Types of stem cells:

The stem cells can be broadly classified into
1) Adult stem cells
2) Fetal stem cells
3) Embryonic stem cells
4) Hematopoietic stem cells
5) Umbilical stem cells 

The adult stem cell is derived from mature organs in the adult individual, fetal stem cell is derived from the fetus developing in the womb and embryonic stem cells are obtained from totipotent cells of early embryo. Depending upon the source of their origin, stem cells from the adult organs or corresponding parts of the fetus can be classified into hematopoietic stem cells that are found in bone marrow and mesenchymal stem cells or the marrow stromal cells which give rise to osteoblast, chondrocytes, adipocytes and even myoblasts in the culture. The hematopoietic stem cells are a continuous source of progenitors of red cells, platelets, monocytes, granulocytes and lymphocytes.

Functions and origin of stem cells;

While some stem cells are pluripotent that is capable of differentiating into many types of cells. Other stem cells derived from specific tissues such as epithelium can sometimes also be unipotent and will differentiate into the specific type required to replenish the cells of the tissue to which these stem cells belong. In other words, stem cells of adult organs may either divide repeatedly to replenish tissue or may remain quiescent. Functionally, the stem cells are multipotent self-renewing cells, which proliferate to make several differentiated cell types of a given tissue in vivo. Embryonic stem cells are, however, extraordinary, since they are totipotent and can give rise to essentially all cell types in the body.