• Stem cells are special human cells that are able to develop into many different cell types.

  • This can range from muscle cells to brain cells. In some cases, they can also fix damaged tissues.
  • Researchers believe that stem cell-based therapies may one day be used to treat serious illnesses such as paralysis and Alzheimer disease.

Types of stem cells:

  • Stem cells are divided into 2 main forms. They are embryonic stem cells and adult stem cells.

Embryonic stem cells:

  • The embryonic stem cells used in research today come from unused embryos.
  • These result from an in vitro fertilization procedure. They are donated to science.
  • These embryonic stem cells are pluripotent.
  • This means that they can turn into more than one type of cell.

Adult stem cells:

  • There are 2 types of adult stem cells.
  • One type comes from fully developed tissues such as the brain, skin, and bone marrow.
  • There are only small numbers of stem cells in these tissues.
  • They are more likely to generate only certain types of cells.
  • For example, a stem cell that comes from the liver will only make more liver cells.
  • The second type is induced pluripotent stem cells.
  • These are adult stem cells that have been changed in a lab to be more like embryonic stem cells.
  • Scientists first reported that human stem cells could be changed in this way in 2006.
  • Induced pluripotent stem cells don’t seem to be different from embryonic stem cells, but scientists have not yet found one that can develop every kind of cell and tissue.

Stem cell potency:

  • On the basis of their differentiation potential, stem cells can be classified into four types: totipotent, pluripotent, multipotent, and unipotent.

Totipotent cells:

  • Totipotent cells can differentiate into all types of cells.
  • For example, the zygote formed during the fertilization of an egg and the first few cells after division are totipotent and have the potential to develop into all types of cells in the body.

Pluripotent cells:

  • Pluripotent cells can develop into almost all types of cells.
  • These include embryonic stem cells, cells derived from the germ layers (mesoderm, ectoderm, endoderm), and cells formed during the early stages of embryonic stem cell differentiation.

Multipotent, oligopotent, and unipotent cells:

  • Multipotent cells can divide into closely-related cells.
  • For example, the hematopoietic stem cells can develop into red blood cells, white blood cells, and platelets.
  • Oligopotent cells can develop into a few cell types, and include lymphoid or myeloid stem cells, while unipotent cells, such as muscle stem cells can only develop into cells of their own type.

Syllabus: Prelims