Stem Cells

Stem cells have provided a new dimension to Regenerative or Reparative Medicine, a promising area of medical science where investigations are made to access the possibility of treatment of diseases through cell-based therapies.

There are over 2-billion human beings throughout the world who are suffering from diseases such as diabetes, osteopetrosis, rheumatoid arthritis, Alzheimer’s disease, heart disease, Parkinson’s disease, spinal cord injuries and different types of cancer. It is believed that these diseases, as well as many more, could be treated, if not cured, through the use of stem cell therapies.

Studies have revealed that stem cells have a remarkable ability to develop into most of the 220 types of cells found in the human body. Researchers believe that due to this property, stem cells extend the greatest potential for the alleviation of human pain.

What are Stem Cells?

Stem cells are undifferentiated precursor cells that retain the capacity to replicate and differentiate into other types of cells. Stem cells are characterized by three unique properties:

• Stem cells are unspecialized cells, that is, they do not have the ability to perform specific functions, such as the ability to secrete hormones into the blood stream like the cells of the endocrine glands or the ability to contract and relax like the muscle cells.
• Stem cells have the ability to proliferate for long periods meaning that these cells can divide many times to produce millions of stem cells.
• Stem cells have the capacity to differentiate into specialized cells such as muscle cells, nerve cells or blood cells.

What are the Different Types of Stem Cells?

Depending upon their developmental potential, stem cells can be segregated into four categories:

1. Totipotent stem cells have the capacity to transform into any type of cell in the human body as well as become any cell of the extra embryonic membranes. However, these stem cells are produced only during the first few divisions of the fertilized egg and cannot produce more copies of themselves.
2. Pluripotent stem cells arise from totipotent stem cells and have the ability to differentiate into any type of body cell except a totipotent stem cell. There are three types of pluripotent stem cells.
   • Embryonic stem cells, which can be retrieved from the inner cell mass of the blastocyst.
   • Embryonic germ cells, which can be extracted from the precursors to gonads in the aborted fetus.
   • Embryonic carcinoma cells, which are found in tetra carcinomas, a type of cancer.
3. Multipotent stem cells can differentiate into limited types of cells that are closely related to one another. For instance, the different types of blood cells: red blood cells, white blood cells and platelets.
4. Unipotent stem cells are so called because they can produce only one type of cell, but they are different from non-stem cells because they have the ability to proliferate.

Where do Stem Cells Come From?

Stem cells can come from one of three main sources: organs and tissue; embryos; and the umbilical cord.

Organs and Tissue

In the human body, bone marrow is considered to be the chief source of stem cells. It contains two types of stem cells: hematopoietic stem cells, which form all types of blood cells, and stromal stem cells, which are responsible for the generation of bone, cartilage, fibrous connective tissue and fat. Apart from the bone marrow, other organs and tissues, such as the liver, skin, brain, skeletal muscles, peripheral blood and blood vessels, also produce stem cells. The stem cells generated by the human organs and tissues are commonly called adult stem cells. These stem cells are believed to reside in a specific area in these organs and tissues. They remain dormant for many years and are activated only when a disease or injury inflicts damage to the tissue. Their main function is to repair and maintain the tissues and organs.

Embryos

The stem cells that are derived from embryos are called embryonic stem cells. For ethical reasons, embryonic stem cells are not retrieved from the egg fertilized in a woman’s body. They are retrieved only from those embryos that are produced by fertilizing the egg in vitro. For the extraction of embryonic stem cells, the embryo must be at least four to five days old, that is, in the hollow blastocyst stage. The blastocyst is made up of three structures: the layer of cells surrounding the blastocyst called the trophoblast; the inner hollow cavity called the blastocoel; and a group of about 30 cells in one part of the blastocoel called the inner cell mass. Human embryonic stem cells are derived from the inner cell mass.

Umbilical Cord

Stem cells derived from the placenta and umbilical cord are called cord blood stem cells. These stem cells are used for the treatment of several diseases, especially those occurring in children. Nowadays, numerous cord blood banks have been established that accept and preserve donated umbilical cord blood, which has made the treatment of many life-threatening diseases possible.

What are the Benefits of Stem Cells?

Stem cells are basically used for intensive studies aimed at acquiring a proper understanding of the various complex events that take place during human development. Once researchers succeed in understanding how genes control these events, they will be able to suggest new therapies for curing diseases, such as cancer. Another area where stem cells can find application is cell-based therapies, where stem cells can be used to generate specific cell types. These new cells can then be used to replace the damaged cells. The replacement of cells, that is, cell-based therapies offer the possibility for the treatment of diseases like diabetes, osteoarthritis, spinal cord injuries and Alzheimer’s disease. Also check out are article on stem cell research ethics and the controversy over stem cells and the ability for cloning.