Regeneration is the process by which organisms replace or restore damaged or lost structures. Some organisms like lizards can regenerate their tails if cut off. For some organisms, entire bodies can be regenerated from small tissue fragments. Regeneration in salamanders involves wound healing, blastema formation from undifferentiated cells, redifferentiation of the blastema into limb structures like digits, and growth to the size of a normal limb. Growth factors stimulate wound healing and regeneration by promoting cell mitosis and blood vessel repair.