Stem cells are special cells in multicellular organisms that are capable of differentiating into a wide range of other cells as needed. In other words, the cells themselves are not specialized, like blood cells, nerve cells, and so forth, but they can make specialized cells to form an embryo or repair damage to an adult organism. This property has suggested that they could be extremely useful in medical treatment, and many nations have established stem cell funding to explore the possibility of research and development.
All multicellular organisms actually start out as a cluster of stem cells. As they divide and multiply, they differentiate themselves to make organs, muscle, bone, and so forth until a complete embryo is formed. Adults also have stem cells, although their precise origin is not fully understood. These adult cells trigger in response to serious injury to replace damaged tissues.
There are three types of stem cells. Embryonic stem cells are taken from an embryo. Cord blood stem cells come from the umbilical cord, which is rich in these cells because it is of fetal origin. Adult stem cells are also known as somatic stem cells, and they are found in a range of locations around the adult body. The exact science and distribution of the adult cells is still a topic of intense research.
In order to be considered a stem cell, a cell must possess two properties. The first is that it must not be specialized for a specific action, but it should be capable of generating specialized cells. In addition, they can replicate themselves numerous times with errors, a process known as proliferation. Research is focused on exploring this unique property, and scientists hope to some day be able to exploit it, stimulating the cells to grow organs for people who need them, for example.
Research on stem cells is controversial in some parts of the world. Embryonic stem cells could only be harvested by destroying an embryo until 2006, when scientists began to prove that lines could be created without this sacrifice. Since some people are uncomfortable with the thought of killing an embryo, this issue raised a great deal of concern among many communities. Other critics are concerned that stem cell research may stray into the realm of cloning, and many communities oppose cloning of human beings for a range of reasons. Most governments have focused on creating clear and understandable legislation about stem cell research, in the hopes of harnessing their immense potential without causing controversy.