regeneration

Regeneration is the process by which organisms replace lost or damaged tissues, organs, or body parts in order to restore function. It is distinguished from repair, where tissue is largely restored but scar tissue remains and function may be incomplete. Regeneration is widespread across life forms, but its extent and mechanisms vary greatly.

In nature, regenerative ability ranges from close to complete restoration to limited tissue replacement. Some invertebrates, such as planarians and hydra, can regenerate entire bodies from fragments. Among vertebrates, salamanders and axolotls can regrow limbs and parts of the spinal cord, while zebrafish can regenerate heart tissue after injury.

Key mechanisms include activation and proliferation of progenitor or stem cells, dedifferentiation of mature cells, and the formation of a blastema, a mass of cells that rebuilds structures. Signaling pathways such as Wnt, FGF, and BMP coordinate cell growth, patterning, and tissue identity during regeneration.

In humans, regenerative capacity is more limited. The liver can regrow after partial removal; skin and bone regenerate, and some nerves can repair slowly. Regenerative medicine seeks to enhance healing with stem cell therapies, tissue engineering, biomaterials, and gene editing to promote functional regeneration.

Plants exhibit extensive regenerative ability, retaining totipotent cells in meristems. They can regenerate organs after wounding and are widely propagated from cuttings or callus cultures.