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Learn about stem cells
THE human body is a complex combination of cells, tissues and organs. Many research studies have been carried out to determine how a single cell is transformed into a group of differentiated and specialized cells. The replacement of damaged cells with new ones has been a promising field of scientific work. This field of research, known as regenerative medicine, is helpful in finding the cure for several diseases.
Cells are the basic functional unit of the body. The human body has some very specialized types of cell called stem cells. Also known as master cells, they have the remarkable ability to produce many types of other cells of the body. The human tissue has a unique group of specialized stem cells that rebuild and replace other cells, for example, nerve cells, heart, lung, skin and insulin-producing cells.
Stem cells perform their function whenever there is wear and tear of the tissue. For example, stem cells in blood, known as haemopoitic, generate blood cells including red blood cells, white blood cells and platelets. The potential sources of haemopoitic blood stem cells are the umbilical cord blood, bone marrow, peripheral blood and embryos. Stem cells divide indefinitely to replenish other cells as long as the person or animal remains alive. When a stem cell divides, it has the potential to remain as a stem cell or turn into another type of cell, with differentiated and specialized functions.
Stem cells have two important properties that differentiate them from other cell types. First of all, they are undifferentiated and unspecialized in nature. This causes self-renewal for long periods of time through cell division. Secondly, they have the ability to turn into specialized functioning cells, under physiological or experimental conditions.
Scientists are working with two types of stem cells in animals and humans — embryonic stem cells and adult stem cells. Embryonic stem cells proliferate during developmental phases and give rise to various organ tissues of the body with rapid and controlled cell division. Adult stem cells form the cell types of the tissue in which they are found. They develop less rapidly as compared to embryonic stem cells. Thus they produce, control and take part in the repair and remodeling of the tissue where ever they reside.
For example, in the bone marrow, blood-forming stem cells give rise to all types of blood cells. However, recent studies have raised the possibility that stem cells from one tissue may be able to produce cell types of a completely different tissue. This property of stem cells is known as plasticity. Examples of plasticity include the formation of brain cells from the blood, liver cells producing insulin and haemopoitic stem cells forming heart cells.
As stem cells do not have any tissue specific structures, this helps them perform specialized functions and give rise to special cells like blood, heart or muscle cells. This process of formation of is called cell differentiation. Scientists are trying to understand the signals present inside and outside the cells which initiate and cause cell differentiation. Various scientific studies have shown that the specific genes of a cell, which are interspersed around the DNA, act as internal signals. They also carry guidelines for all structures and functions of a cell. External signals include various chemicals secreted by other cells, physical contact with surrounding cells and some molecules of the micro environment around the cell.
There are three classes of stem cells: totipotent, multipotent and pluripotent. A fertilized egg is totipotent, with the potential to give rise to all different types of cells. Multipotent are cells which form a small number of different types of cells. Finally, pluripotent are those which give rise to any cell type in the body except those cells needed to form the fetus (the biological name for an unborn child after the eighth week of pregnancy).
For purposes of scientific research, pluripotent stem cells are obtained from a human embryo that is a few days old. They can be used to form cell cultures that can be grown indefinitely in the laboratory. Once a stem cell culture or stem cell line has been formed in the body, it becomes immortal till the body is alive.
That’s why stem cells cultured in laboratories can be either stored or distributed to other researchers. It also helps scientists to work on them for use in transplantation or treatment of diseases. In future, scientists will be able to change or modify human stem cell lines in laboratories with the help of gene therapy or other techniques. They will also be able to replace damaged genes and introduce new genes to stem cells. This will equip stem cells with properties required for treating various diseases.
Scientists and doctors consider stem cell research as a remarkable achievement of modern science, as they can be successfully used in different health and medical researches. Some of the most severe medical conditions, such as cancer and birth defects, are also due to problems and changes in stem cells. A better understanding of normal cell development will help scientists understand and find the cure of many such medical conditions.
Stem cells can also be used as a renewable source of replacement cells and tissues to treat spinal cord injury, stroke, burns, heart diseases, diabetes, osteoarthritis (bone disease), rheumatoid arthritis (joint disease), including Parkinson’s and Alzheimer’s disease.
Till now scientists have not been able to treat any major disease with stem cell research. This is because of the lack of funds required to perform such complicated and time-consuming procedures. That’s why the United States government has announced special funds to support laboratories working on stem cell technology.
The only type of stem cells currently being used to treat human diseases is blood-forming stem cells present in the bone marrow. It has helped in the treatment of blood disorders like leukemia, lymphoma (a cancer of a type of white blood cells known as lymphocytes) and other inherited blood diseases.
Since a lot of research is being done on stem cells, it is quite possible that cell-based therapies could be a routine treatment plan for physicians in future. Furthermore, it would help in the screening of new drugs and chemical toxins.
The writer
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