Stem Cell Basics – Introduction:
You may be amazed by the fact that human body is made up of approximately 35 billion of cells and these cells are categorized into approximately 200 terminally differentiated or matured cell types. These terminally differentiated or matured cell types are highly specialized, and have an ability to perform specific tasks or functions in a multicellular organism. All terminally differentiated cell types have common origin, ie from “Stem Cell”. Cells that have an ability to divide and differentiate into terminally differentiated or matured cell types and tissues are termed as Stem Cells.
Stem cells differ from other cells types by two important characteristics:
- They are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity.
- Under certain physiologic or experimental conditions, they can be induced to become tissue or organ-specific cells with special functions.
Once terminally differentiated or matured cells are formed, they lost their ability to divide further and observe a truncating life span. For example enterocyte, specialized for absorption of nutrients are alive for 4-6 days and red blood cells maintain functionality for 120 days. It is also observed that even those specialized cells that have not lost the ability to divide can undergo cell cycle for only 50–60 times (Hayflick limit).
In order to maintain the structure and function of tissues composed of cells that die or have a limit in their mitotic activity, pools of defective cells or dead cells should be replaced with young and healthy cells. This replacement activity is carried out by stem cells. They serve as the body’s repair system by revitalizing themselves and replenishing more specialized cells in the body. This capability of stem cells to replace dead or defective cells helps in the treatment of patient suffering from disease or defects. In organs, such as the gut and bone marrow, stem cells divide to repair and replace defective or damaged tissues. In other organs such as pancreas and heart, stem cells only divide under some special conditions.
Based on their ability to differentiate, stem cells are classified into 3 main categories, they are:
- Totipotent: Cells that has an ability to develop into a new individual are called totipotent cells. Eg: cells from early embryos.
- Pluripotent: Cells that are capable of forming any (Approximately 200) cell types are called Pluripotent cells. Eg. Some cells of blastocyst (5 to 14 days)
- Multipotent: Specialized cell types that is produced from pluripotent stem cells. Eg. Fetal tissue, cord blood, and adult stem cells.
Stem cells are considered as very important for Human beings in many ways. When the embryo is 3-5 days old, it is called blastocyst, the inner cells forms the whole body of the organism, including specialized cell types and organs such as the heart, skins, lungs, eggs, sperms and other tissues.
Along with unique regenerative abilities, stem cells also offer new potentials for treating diseases such as diabetes, and heart disease. However, much work has to be carried out in order to understand how to use these cells for cell-based therapies and also to treat disease, which is also referred to as regenerative or reparative medicine.
Research on stem cells helps scientists to learn more about the stem cells essential properties and what that make stem cells different from specialized cell types. Currently researchers and scientists are using stem cells to develop and screen new drugs and also to prepare fresh model systems to examine normal growth and identify the causes of birth defects.
Stem cell research is considered as one of the most fascinating areas of biology. But! Its popularity raises scientific questions and controversies as frequently as it generates new discoveries.