What Are Stem Cell?

STEM CELL WHAT ARE STEM CELL? All of us start from a single cell formed at conception, when a sperm cell joins with an egg. This cell then starts dividing and forms a ball of cells. About four days after conception, this ball of cells is smaller than a pinpoint. This process, called differentiation, allows some cells to become liver cells and other cells to become nerve cells or skin cells and so on. This earliest stem cell in the embryo gives rise to all the different cells in the body. WHAT ARE THE DIFFERENT KINDS OF STEM CELL? When the embryo is less than four days old, its cells are called totipotent stem cell that is, they still have the total potential and can form a human being if they were separated and implanted individually into a woman uterus. After four or five days, the cells are pluripotent- that is, they still have the potential to form virtually every cell in the body but can no longer form an entire human being by themselves. As the cells continue to divide into more cells, they become mulipotent- that is, they have the potential to form several different kinds of cells, but not all kinds of cells. WHAT 'S THE DIFFERENCE BETWEEN ADULT STEM CELLS AND STEM CELLS TAKEN FROM AN EMBROY? Embryonic stem cells are stem cells that you take from an embryo, and adult stem cells are stem cells you take from a person (adult or child) or from the umbilical cord. Scientists have also found that a few tem cells persist even after we are born. It seems that these adult cells are of backup, so if a particular kind of cell needs replacing, the adult stem cells can differentiate and form those cells. Most adult stem cells are multipotent and can form a limited number of cell types. WHY NOT JUST DO RESEARCH ON ADULT STEM CELLS? Adult stem cells definitely have some advantages over embryonic stem cells. First, most people have no ethical problem with using them. Second, these are cells from your own body, so your immune system will probably not try to reject them. If you use cells that are not part of your body, your body's immune system may see them as intruders and try to kill them. But scientists have found three main disadvantages to using adult stem cells. First, these are multipotent (more mature) cells. They can form several types of cells-for example, recent experiments with animals showed that stem cells from the blood can form skin cells, liver cells, and others, but they do not