Embryonic stem cells(ES cells) are undifferentiated cells from the early blastocyst (about 5 – 7 days after fertilization). Blastocyst contains about 140 cells. The appearance is a layer of flat cells—trophoblast that can develop into embryonic tissues such as placenta. The center cavity is called blastocyst cavity. Cells inside of the cavity are called inner cell mass. These undifferentiated cells can be further divided, differentiated and developed into individuals. Inner cell mass begins to differentiate when forming three germ layers. Each layer will differentiate into corresponding tissue and organ of the body. Ectoblast for the skin, eyes and nervous system, mesoderm for bone, blood and the muscle, endoderm for liver, lung and intestine. Because inner cell mass can develop into a complete individual, and these cells are thought to be totipotent. When the cells cultured in a dish, we call them embryonic stem cells.
Human stem cells have the ability of self replication, and can differentiate into 206 kinds of human tissues and organs. Embryonic stem cells come from during the embryonic development of the embryo sac in the inner layer of cells. Embryonic stem cells differentiate to form specific stem cells, blood stem cells can differentiate into red blood cells, white blood cells and platelets, skin stem cells can form a variety of different types of skin cells. In addition, the cells in the tissues of fetuses, adults and children are called pluripotent stem cells. Embryonic stem cells can be propagated and have the advantage of pluripotency, so they have broad application prospects in theory . But in fact due to xenogenic embryonic stem cells and their differentiation of tissues and cells can cause immune rejection in clinical treatment, so there needs a long-term immunosuppressive therapy based on embryonic stem cells. In addition, embryonic stem cells are extracted from embryo, but in theory, there causes controversy. Technically, it is unable to control embryonic stem cells to differentiate into specific cells, so it easily leads to teratoma. Adult stem cells don’t induce teratoma, but the efficiency is not ideal. So the embryonic stem cells and adult stem cells each have their own advantages and disadvantages. They are certainly able to differentiate in vitro .
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