More Views of stem cell

stem cells do not serve any one function, many have the capacity to serve any function after they are instructed to specialize. Every cell in the body for example is derived from first few stem cells formed in the early stages of embryological development.Stem cells extracted from embryos can be induced to become any desired cell type. Stem cells are distinguished from other cell types by two important characteristics. First- they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity.Second- under certain physiologic or experimental conditions they can be induced to become tissue or organ-specific cells with special functions.Such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues In some organs.Such as the pancreas and the heart, stem cells only divide under special conditions in other organs.Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old embryo called a blastocyst, the inner cells give rise to the entire body of the organism, including all of the many specialized cell types and organs such as the heart, lung, skin, sperm, eggs and other tissues. Scientists are already using stem cells in the laboratory to screen new drugs and to develop model systems to study normal growth and identify the causes of birth defects.Stem cells are capable of dividing and renewing themselves for long periods.The specific factors and conditions that allow stem cells to remain unspecialized are of great interest to scientists. It has taken scientists many years of trial and error to learn to derive and maintain stem cells in the laboratory without them spontaneously differentiating into specific cell types.

Stem cells can give rise to specialized cells. When unspecialized stem cells give rise to specialized cells, the process is called differentiation. While differentiating, the cell usually goes through several stages, becoming more specialized at each step. Scientists are just beginning to understand the signals inside and outside cells that trigger each stem of the differentiation process. The internal signals are controlled by a cell's genes, which are interspersed across long strands of DNA, and carry coded instructions for all cellular structures and functions. Adult stem cells typically generate the cell types of the tissue in which they reside. For example, a blood-forming adult stem cell in the bone marrow normally gives rise to the many types of blood cells.Adult stem cells, and tissues derived from them, are currently believed less likely to initiate rejection after transplantation. This is because a patient's own cells could be expanded in culture, coaxed into assuming a specific cell type and then reintroduced into the patient. The use of adult stem cells and tissues derived from the patient's own adult stem cells would mean that the cells are less likely to be rejected by the immune system.Stem cells can now be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture. Highly plastic adult stem cells from a variety of sources, including umbilical cord blood and bone marrow, are routinely used in medical therapies.