Stem cells are undifferentiated cells that have the capacity and potential to develop into specialized-functioning cells. They are known as the “mother cells,” due to their ability to replenish tissue and regenerate organs. The two types of stem cells are embryonic and somatic (adult) cells. Embryonic stems cells (ESCs) have not been differentiated, whereas somatic adult cells (ASCs) have. In other words, embryonic stem cells can be coded to become any specific cell required by the body. Adult stem cells, however, are limited within the confines of certain functions. Because of this, embryonic stem cells are more useful to scientists due to their flexibility in use.
Embryonic stem cells are classified into four groups “based on their potential to generate different cell strains” (Arce). These four categories are totipotent, luripotent, multipotent and tissue-progenitor cells. Totipotent and luripotent are found in embryos and multipotent and tissue-progenitor cells are found in adult organisms. Totipotent cells are the most flexible, because of their capability to generate all human cells, such as heart, liver, blood cells or even an entire organism. They are created when the sperm fertilizes the egg and produces a diploid known as zygote. As the zygote undergoes several cell divisions, more totipotent cells are created. After approximately four days the blastocyst, which has an inner mass cell and makes the embryo, is formed. Pluripotent cells begin forming from the