Shri.S.Ramakrishnan, Inspector of Customs, Trichy is the author of this article. This youngster is an Engineering Graduate in Computer Science. He has thirst to acquire knowledge on new technologies, fianance and investments and of course in the field of information technology.
What are Stem Cells ?
As we know, all the living things on earth are made up of cells. Starting from bacteria (single-cell organism) to human beings (multi-cell organism), every single life consists of at least one cell. The difference between unicellular and multi-cellular organism lies in the way they function. In a unicellular organism, all the functions of the organism are performed by the single cell. But in a multi-cellular organism, the functions of the organism are done by many specialized organs. For example, we sense the world through our sense organs (i.e., eyes, ears, nose, tongue and skin) and the circulatory system is taken care of by various organs like heart, vessels (arteries and veins) etc., These organs are evolved in such a fashion that they can only do some particular specialized functions. And, they are incapable of doing any other function which they are not meant for. An eye cannot pump the blood nor can a heart see.
Your Normal Cells are specialized that is they are not capable of doing any new functions:
Every organ that forms a part of a system in our body is assigned with some particular work, and obviously the cells that build a particular organ are specialized in doing a particular function. A cell that is in the eyes knows only how to react to light. Likewise, a cell in kidney knows only how to filter. The cells’ ability to grow, reproduce and repair is guided by the genetic codes written in the cells themselves. Every cell has got chromosomes (made-up of ‘De-oxy Ribonucleic Acid’), which is a genetic material that determines what a cell should do and how. The cell cannot function beyond the limitation set up by the chromosomes.
Organs that do not reproduce and those reproduce all through our life:
Most of the organs mature in the early stage of life, and they stop growing after that. So, cells of the matured organ do not have the ability to reproduce themselves. For example, cells of a matured brain do not reproduce. Once a brain cell is dead, it won’t be replaced by another brain cell. Same is the case with bones. When they are fully grown they won’t produce any new cells. Organs like these have got mechanisms to repair themselves. At the time of repairing, new cells do grow in these organs. But, the growth of new cells is triggered by the organs only when they get damaged. There are certain organs in our body which produce new cells continuously at regular intervals. For example, both the red blood cells and white blood cells are produced all through our life.
What happens if specialized cells that don’t reproduce get damaged?
Now, as we said the cells of many organs of our body are specialized to do a particular function, and they lose their ability to produce new cells once they are matured. So what happens if the cells of these organs get damaged? The organ starts mal-functioning i.e., they don’t work properly. This mal-functioning of cells causes variety of diseases. Is there any way to cure the diseases caused by the improper functioning of cells? The answer is ‘no’ as there is no way for us to interfere in the internal functioning of a cell. The cells that cause trouble may simply be killed, as in the case of treatment of cancer. Using techniques such as irradiating (exposing the cells to rays which kill them) the damaged cells, we get rid of them.
Can we replace the specialized cells that are damaged?
Given that there is no way correct the functions of damaged cells, Can’t we replace the damaged cells by fresh ones? Answers to these questions are ‘Stem Cells’. What are ‘Stem Cells’ actually? In simple terms, the cells that make up our body are specialized i.e., they can only perform the functions they are assigned to do. But, the ‘Stem Cells’, on the other hand, are not specialized. It possess the potential to change into any ‘specialized cell’ of our body. Sounds interesting! Is it not? ‘Specialization’ is not always a good thing. In a sense that, most of the times it is very difficult to get out of the ‘Specialization’. For example, you know only to efficiently drive a car and you have been driving cars throughout your life. What happens if you are asked to do cooking? The possibility is that either you won’t accept to do cooking i.e., which you have never done, or you may be incapable of doing cooking. But, when you are not specialized in a particular field you possess the potential to learn and do any other work. Stem Cells are like ‘Tabula Rasa’ (a blank slate). The ’blank slate’ is ready to be written on. under certain physiologic or experimental conditions, they can be induced to become tissue- or organ-specific cells with special functions. This means that the stem cells can remain inactive for a long period and then start functioning i.e., they reproduce themselves through cell division. And, the stem cells, which are unspecialized’, can be made into ‘specialised’ cell of any organ of our body. It is also evident that there are stem cells in our body already, and our body utilises stem cells to repair some of the damaged organs like gut or bone marrow.
Have look at this interactive animation below that would exactly let you know what a stem is all about.
Types of Stem cell based on their potency:
Totipotent Stem Cells:
‘Toti’ means ‘whole’ or ‘entire’. As the name indicates, this type of stem cell is capable of developing into any other type of body cell. It is possible to make an entire organism from this totipotent stem cells. When a sperm cell from male and an egg cell from female unite (fertilisation), they combine to form a new cell called ‘Zygote’. ‘Zygote’ is the first cell from which an organism develops. This ‘Zygote’ is ‘totipoent stem cell’. ‘Zygote’ develops into ‘embryo’. Approximately for the first four days after the sperm cell and egg cell unite to form a ‘Zygote’ (which is ‘Totipotent’), it multiplies itself by cell division i.e, a cell divides itself into two cells which are identical. For these first four days after fertilisation, all the cells of a developing organism (i.e, in the uterus) are ‘Totipotent’. After these four days, the totiptent cells specialise to some extent and produce ‘Pluripotent Stem Cells’.
Pluripotent Stem Cells:
This type of stem cell is almost as potent as totipotent stem cells, and they are also capable of developing into any other type of body cell. The only difference is a totipotent cell can make an entire organism including ‘placenta’ whereas a pluripotent stem cell cannot make ‘placenta’.
Multipotent Stem Cells:
This type of stem cell are capable of developing into one of several cell types in a given “family” of cell types. For example, a blood stem cell can become any of the many types of blood cell (red blood cells, white blood cells, platelets, etc.), but cannot become a muscle cell or a nerve cell.
Unipotent Stem Cells:
This type of stem cell, as the name suggests, is capable of becoming only one type of cell. And, this type of stem cells is found in our body in the organs where continuous replacement of cells happens. Skin is a good example where skin cells regularly die and new skin cells grow. So, the potential of this stem cell is least among all the types of stem cells.
Stem Cells can mainly be obtained from two sources:
- Our Body (Adult Stem Cells)
Embryonic Stem Cell:
This type of stem cells is obtained from the embryos. In humans, from the time of conception i.e., the union of sperm cell and egg cell to form ‘Zygote’, up-to the fourth week, the organism (baby!!) is called Embryo. This Embryo is rich of stem cells that too pluripotent cells. So can’t we reap stem cells we need from the embryos? Yes, it is possible. But, there arises a ethical question. Whether destroying the further growth of embryo, which is a growing living organism, to get stem cells amounts to killing? Some argue that as embryos neither has any specialised organ like heart, brain or kidney nor they have the ability to sense, there is nothing wrong in taking stem cells from embryo. Others argue, even though it could not sense it amounts to killing it as they have the ‘potential’ to grow. The argument goes on.
Adult Stem Cells:
Most of the organs of our body have stem cells at least to some extent. Bone Marrow (centre of our bones) has stem cells which can make all the types of blood cells at regular intervals. Some organs like brain and heart have less number of stem cells. But the stem cells in these organs do not make new cells. This is the major challenge in the medical science today.
If these stem cells start responding when the organs get damaged and grow new cells, probably most of the diseases could be cured very easily. Scientists are now trying to find ways to activate these stem cells (which are there in our body and remain inactive).
Can we create new organs out of preserved stem cells?
The entire research activities on stem cells revolve around this idea. Take a pluripotent stem cell derived from any source, just engraft (similar to injecting) it into a damaged or diseased organ, new cells grow and the organ gets renewed. Sounds simple, but the process of doing it is now only a theoretical possibility.
What can be done now by us?
Stem cells are also obtained from the umbilical blood. When the umbilical cord is cut to separate a child from the uterus of a mother, the umbilical cord bleeds and this blood is rich of stem cells. The potency and usage of such stem cells are being examined by the scientists now. There are now blood banks in many places to store these umbilical stem cells. But it is better to store this umbilical blood, as the child may require it in future to get cured from many diseases as medical science is growing in a faster pace in this direction. One more advantage is this the easiest way to obtain stem cells.