All animals have the ability to regenerate tissue and repair their body after it has been damaged or a part of the body has been lost—to varying degrees. Higher vertebrates, including mammals, are able to regenerate only very small parts of their bodies, such as portions of skin or muscle, while lower animals can regenerate entire body parts. Dugesia tigrina, or brown planaria, can regenerate a whole body from a piece one-eighth the size of its original body.
Regeneration consists of three basic processes, that sometimes occur simultaneously and at other times sequentially at the site of the injury:
- Loss of differentiation in tissues near the injury and migration of new cells to the injury, resulting in a mass of undifferentiated tissue at the site.
- Redifferentiation of cells into various tissues.
- Reorganization of tissue into the original form by differential growth (the growth of newly generated tissues at different rates than the rest of the body’s tissues.)
