How does biological regeneration replace lost or damaged body parts?

Biological regeneration is the process by which organisms replace or restore lost or damaged body parts. This capability varies significantly across species, ranging from the simple healing of wounds to the complex regrowth of entire limbs.1

Mechanisms of Regeneration

When an appendage is lost, many organisms utilize a specialized mass of undifferentiated cells called a blastema to facilitate regrowth. The formation of a blastema typically involves the following steps:2

• Dedifferentiation: Tissues at the site of the injury, such as muscle or bone, lose their specialized characteristics and revert to an embryonic-like state.23
• Blastema Formation: These dedifferentiated cells migrate and accumulate beneath the wound epidermis, forming a bud-like structure.3
• Proliferation and Differentiation: Cells at the tip of the blastema multiply, while those closer to the stump differentiate into the necessary tissues—such as muscle or cartilage—to gradually reform the lost structure.3

Alternative Processes

Not all regeneration relies on blastema formation. Some organisms employ compensatory hypertrophy, where remaining tissues enlarge to restore function without replacing the missing parts, such as when a human liver regrows after partial removal. Additionally, through metaplasia, one type of tissue can be converted into another to replace a lost structure, as seen in the development of a new lens from iris tissue in certain amphibians.1