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Stem cells are a class of undifferentiated cells that are able to differentiate into specialized cell types.Stem cells are biological cells found in all multicellular organisms that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells.There are two broad types of stem cells: embryonic stem cells Cheap Authentic Jerseys , which are isolated from the inner cell mass of blastocysts and adult stem cells which are found in various tissues in mammals.Stem cells and progenitor cells act as a repair system for the body, replenishing adult tissues in adult organisms.Stem cells can differentiate into all the specialized cells but also maintain the normal turnover of regenerative organs such as blood, skin Cheap Jerseys , or intestinal tissues in a developing embryo.Stem cells can now be artificially grown and transformed into specialized cell types with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture. Embryonic cell lines and autologous embryonic stem cells generated through therapeutic cloning have also been proposed as promising candidates for future therapies.Stem cells are categorized by their potential to differentiate into other types of cells. Embryonic stem cells are the most potent since they must become every type of cell in the body. The full classification includes:

Totipotent - the ability to differentiate into all possible cell types. Examples are the zygote formed at egg fertilization and the first few cells that result from the division of the zygote.

Pluripotent - the ability to differentiate into almost all cell types. Examples include embryonic stem cells and cells that are derived from the mesoderm, endoderm, and ectoderm germ layers that are formed in the beginning stages of embryonic stem cell differentiation.

Multipotent - the ability to differentiate into a closely related family of cells. Examples include hematopoietic (adult) stem cells that can become red and white blood cells or platelets.

Oligopotent - the ability to differentiate into a few cells.

Unipotent - the ability to only produce cells of their own type Washington Redskin Throwback Jersey , but have the property of self-renewal required to be labeled a stem cell.

People also take issue with the creation of chimeras.A chimera is an organism that has both human and animal cells or tissues. Often in stem cell research, human cells are inserted into animals and allowed to develop. This creates the opportunity for researchers to see what happens when stem cells are implanted. Many people object to the creation of an organism that is "part human".Embryonic stem cells are considered pluripotent instead of totipotent because they do not have the ability to become part of the extra-embryonic membranes or the placenta. A stem cell must be able to produce new blood cells and immune cells over a long term, demonstrating potency. It should also be possible to isolate stem cells from the transplanted individual which can themselves be transplanted into another individual without HSCs Tennessee Titans Throwback Jersey , demonstrating that the stem cell was able to self-renew.Stem cells are either extracted from adult tissue or from a dividing zygote in a culture dish. Once extracted, scientists place the cells in a controlled culture that prohibits them from further specializing or differentiating but usually allows them to divide and replicate. The process of growing large numbers of embryonic stem cells has been easier than growing large numbers of adult stem cells but progress is being made for both cell types.

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