Understanding stem cells

There is more to stem cells than what meets the eye

Understanding stem cells

Stem cells are cells that have the ability to turn into other specialised types of cells. For example, a stem cell can turn into liver cells, skin cells, nerve cells etc.,

In other words, just like how the plant stem produces leaves, flower and fruits, stem cells are capable of producing other cells in our body.

Stem cells are responsible for bodily repair as well as the growth, for example, of a limb or tail of a lizard after it is cut off from its body.

Types of stem cells

Stem cells are of two types: those arising from the embryo/foetus and from the adult animal.

  • Embryonic stem cells. Embryo is the mass of cells formed a few days after fertilisation of the egg. Stem cells derived from embryo are totipotent – they can become any kind of cell in the body.
  • Foetal stem cells. After the eighth week of development in the mother’s womb, the embryo is referred to as foetus. By this time it has developed a human-like form. Stem cells in the foetus are responsible for the initial development of all tissues before birth. Like embryonic stem cells, foetal stem cells are pluripotent [descendants of the totipotent stem cells].
  • Umbilical cord stem cells. The umbilical cord is also a source of stem cells. After birth, the umbilical cord is removed from the infant, leaving a bellybutton in its place. Blood from the umbilical cord contains stem cells that are genetically identical to the new-born child. Umbilical cord stem cells are multipotent, meaning they can differentiate into a limited range of cell types.
  • Adult stem cells. These are undifferentiated cells found in the liver, skin, bone marrow and brain etc., which have the capability of repair and renewal. They can also yield all the specialised cell types of the tissue from which they originated. Adult stem cells are multipotent.


As mentioned earlier, stem cells are responsible for the repair of our body when there is an injury. A good example is regrowth of the whole limb or tail when a lizard is severed. In human beings, repair from normal everyday wear and tear is accomplished by the resident stem cells. However, under abnormal circumstances these nests of cells grow even when not needed and form tumours and cancer.

The application of stem cells is now gaining solid ground. Some examples:

  • The use of stem cells for the testing of new medicines, especially in cancer
  • To provide cells and tissues required for the renewal or repair of body organs in diseases such as cancer, spinal cord injuries, Parkinson’s disease, Alzheimer’s disease, stroke, glaucoma, corneal ulcer, macular [eye] degeneration leading to blindness etc.,

Ethical, legal issues

  • Harvesting stem cells destroys the embryo which may pose obvious ethical obstacles to their use in research. Although in most cases the embryos would otherwise be discarded, the question remains as to whether the extraction of embryonic stem cells from such embryos is justified
  • Legal issues require researchers and the public to help policymakers decide whether and how stem cell technologies should be regulated by governments

The future’s bright

Researchers and physicians are now working to design stem cell therapies that are more effective, and also capable of reducing certain risks to patients. Cells that are donated by one person and used by another person raise the possibility of donor cell rejection by the patient’s immune system. In the future, it may be possible for a person to use a sample of his or her own stem cells to regenerate tissue. This will help reduce or even eliminate the danger of rejection.

It may also be ethically possible to direct stem cells already present in our bodies to the necessary cell fates without the need to isolate and/or culture them.


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Madhuri Behari is Professor & Head, Department of Neurology, All India Institute of Medical Sciences [AIIMS], New Delhi.


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