Cells that remain as sources of other cells are called

They are called stem cells. This cells are undifferentiated which means it can specialize in other types when it receives the right stimuli. They can divide through mitoses and become more stem cell or become a bone, muscle, blood cell, etc.

They can have 2 origins: embryos or some human tissue; their function is to regenerate or substitute damaged cells

No it doesnt because it can be any number.