At the time of XCI, a certain number of the cells in the body are precursors to the pluripotential embryonic stems cells.
Stem cells are vital to the development of an organism.
Throughout the life of an individual, stem cells regenerate themselves as well as develop into cells that form the blood, lymphoid and many other systems. Stem cells not only supply the progenitor cells to these systems at the respective stages of development, but also supply them with replacement cells further in life when there is a depletion of a certain kind of cell pool. At this point in time, the n 1 HSC begin to divide and die for t 1 generations, keeping a pool of HSC in the body throughout life. Thus, some of the HSC that we have at age 70 are the same cells that we had at birth. Meanwhile, some of the HSC are sampled to become differentiated blood cells.