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Stem cells involve precursor cells that can give rise to multiple tissue types. It is generally expected that human embryonic stem (ES) cells will serve as an experimental model for studying early development in our species, and, conversely, that studies of development in model systems, the mouse in particular, will inform our efforts to manipulate human stem cells in vitro.

Human embryonic stem (ES) cells have been the subject of many review articles since the first report of their derivation over five years ago (Thomson et al., 1998), and the characteristics of the cells, their potential use in regenerative medicine, and the ethical issues surrounding their provenance, have been widely discussed in the scientific literature. However, few reviews have focused on ES cells from an embryological standpoint. We now have an experimental system that provides us with routine access to stages of the human life cycle that were previously out of reach to experimentation.

Stem cells are undifferentiated cells which have the ability to divide for indefinite periods in culture and give rise to specialized cells on differentiation. Cells forming a whole conceptus are termed totipotent; whereas pluripotent cells have the ability to contribute several tissues of the foetus. Multipotent somatic stem cells, isolated from foetal and adult tissues, differentiate into effector cells of their tissue. However, recent studies imply that adult stem cells can also generate cell types of heterologous tissues indicating broad differentiation potentials.

A flurry of startling discoveries in stem cell biology has shattered preconceptions about how cell specialization are controlled in the body and has boosted this field to the top scientific, political, and commercial agendas. The excitement has raised the hope that the long sought goal of being able to regenerate human tissues may be closer than had been thought. In this review, we discuss recent advances in our understanding of both embryonic and adult stem cells.

Types of Stem Cells

Embryonic Stem cells:


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