Stem cells are cells that have the inherent ability to develop into many different or specialized cell types. They renew by mitotic division and also are able to divide and become specialized cells of the body such as liver cells, muscle cells, blood cells, and other cells with specific functions. The process of changing into a specific cell type is known as differentiation and before differentiating into specialized cells they are often termed as undifferentiated cells. In some areas of the body, stem cells divide regularly to renew and repair the existing tissue. The bone marrow and gastrointestinal tract are examples areas in which stem cells function to renew and repair tissue.

These stem cells are special because they renew and divide themselves even after long period of inactivity. By this continuous division they repair and replace worn out or damaged tissues. In some organs, such as the gut and bone marrow, stem cells regularly divide. In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions.

The best example of a stem cell in humans is that of the fertilized egg, or zygote. A zygote is a single cell that is formed by the blend of a sperm and ovum. The sperm and the ovum each carry half of the genetic material required to form a new individual. Once that single cell or zygote starts dividing, it is known as an embryo. One cell becomes two, two become four, four become eight, eight to sixteen, and so on; doubling rapidly and forms an a organism .The structure of the organism consists of many billions of cells with functions as diverse as those of your eyes, your heart, your immune system, the color of your skin, your brain, etc. All of the specialized cells that make up these body systems are progeny of the original zygote, a stem cell with the potential ultimately develop into all kinds of body cells. The cells of a zygote are totipotent, meaning that they have the capacity to develop into any type of cell in the body.


Stem cells can be classified into three broad categories, based on their capability to differentiate. Totipotent stem cells are found only in early embryos. Each cell can form a complete organism (e.g., identical twins). Pluripotent stem cells exist in the undifferentiated inner cell mass of the blastocyst and can form any of the specialized cells of the body. Multipotent stem cells are derived from fetal tissue, cord blood and adult stem cells. Even though their ability to differentiate is more limited than pluripotent stem cells. The sources of stem cells are the following :
1. Embryonic stem cells : They are undifferentiated inner mass cells of a human embryo usually seven to ten days after fertilization
2. Fetal stem cells -They are taken from the germline tissues that will make up the gonads of aborted fetuses. The fetus contains stem cells that are pluripotent . The embryo is referred to as a fetus after the eighth week of development
3. Umbilical cord stem cells - Umbilical cord blood contains stem cells similar to those found in bone marrow.
4. Placenta derived stem cells -Nearly ten times stem cells can be harvested from a placenta as from cord blood.
5. Adult stem cells - Many adult tissues contain stem cells that can be isolated. These are stem cells that are largely tissue-specific in their location. They are specialized in their functions. Hence known as multipotent stem cells. Adult stem cells are sometimes referred to as somatic stem cells. The best characterized example of an adult stem cell is the blood stem cell (the hematopoietic stem cell).

The process by which stem cells tend to become differentiated, or specialized, cells is complex and involves the regulation of gene expression. Research is ongoing to further understand the molecular events and controls necessary for stem cells to become specialized cell types.


As stem cells renew and differentiate into specialized cells, this ability is been used by the medical science to cure some health defects. Some of the most serious medical conditions, such as cancer and birth defects, are due to problems that occur in the process of differentiation . Stem cells are also transplanted into a damaged body part and directing them to grow and differentiate into healthy tissue. Unfortunately, the number of people needing a transplant far exceeds the number of organs available for transplantation. Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues to treat a myriad of diseases, conditions, and disabilities including Parkinson's disease, amyotrophic lateral sclerosis, spinal cord injury, burns, heart disease, diabetes, and arthritis.
Recently, umbilical cord blood stem cells have been used to treat different cancer like such as leukemia and lymphoma. During chemotherapy, most growing cells are killed by the cytotoxic agents. These agents, however, cannot discriminate between the leukemia or neoplastic cells, and the hematopoietic stem cells within the bone marrow. Hence even the healthy cells that serve as the immune system gets destroyed during this process. It is this side effect of conventional chemotherapy strategies that the stem cell transplant attempts to reverse; a donor's healthy bone marrow which is immunologically matched is injected into the patient. The transplanted stem cells populate the receiver's bone marrow and begin producing new, healthy blood cells.
Umbilical cord blood stem cells and peripheral blood stem cells can also be used instead of bone marrow samples to repopulate the bone marrow in the process of bone marrow transplantation.


Stem cell research offers great promise for understanding basic mechanisms of human development and differentiation, as well as the hope for new treatments for diseases such as diabetes, spinal cord injury, Parkinson's disease, and myocardial infarction. However; there is widespread controversy over the use of human cells, as it is directed at the body's non-reproductive cells, it should only affect the genetic makeup of that one individual, and not be passed on to any children they may subsequently have. In contrast, any genetic changes in the reproductive cells before the stage of differentiation of the embryo into reproductive and non-reproductive cells, would affect all future offspring of that person. This makes a vital ethical issue. It has major philosophical, moral or religious oppositions.
Is it acceptable for human beings to manipulate human genes?
Are we Playing God?

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I have done biotech in my under graduation and it interests me still.