What does totipotent mean?


Totipotent means that each cell can give rise to all the 220 cell types in the embryo plus the extra-embryonic tissues necessary to form the placenta that together allow for the development of the fetus. The ability to form the placenta is a defining feature of totipotent cells.

As the embryo travels along the oviduct, the cells continue to proliferate and the morula develops into a blastocyst that contains a cavity. The outer layer of cells of the blastocyst will go on to form the placenta and other supporting tissues needed for fetal development in the uterus. The inner cell mass of cells located at the polarized end of the cavity contain the pluripotent stem cells. These cells are of particular interest to researchers and others as they will eventually mature to form virtually all of the tissues in the human body.


[Figure 2 Illustration/diagram of Differentiation - Potential replacement (LEAVE OUT UNTIL WE RECEIVE REPLACEMENT SUGGESTION)]




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Figure 3: Closed - Two mouse embryos at the blastocyst stage. Open - Color-enhanced image of a human embryo at the blastocyst stage opened to reveal the inner cell mass.

This is a picture of a blastocyst, caught on the head of a pin. In the picture on the right, the blastocyst is opened revealing the inner cell mass containing the stem cells.

What does pluripotent mean?


What is important to know here is that while the inner cell mass cells can form virtually every type of cell found in the body, and therefore the cells are considered pluripotent, they cannot form an entire organism because they are unable to give rise to the placenta and other tissues necessary for gestational development in the uterus. This is a key point. Because their potential is not total, they are not totipotent – only totipotent cells can go on to develop into a fetus. Pluripotent cells will form every cell in the body but will never form an embryo.

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