tissue regeneration

Tissue regeneration is the body regrowing what it lost back to its full working form, with the right cells in the right places — not just plastering over the gap with a scar. It is the difference between repainting a damaged car door and forging an identical new one. When a tissue truly regenerates, you often cannot tell afterward that anything was ever missing.

Our bodies do this unevenly. The liver can regrow a large chunk of itself, skin and the gut lining renew constantly, and blood is remade every day. But many tissues, like heart muscle and most of the nervous system, barely regenerate in adults and patch the damage with scar instead. Why some tissues rebuild and others give up is one of the field's central questions.

Other animals put us to shame: a salamander can regrow an entire amputated limb, complete with bone, muscle, and nerve. Studying how they do it — and why we mostly cannot — is a major route toward coaxing human tissue to rebuild rather than scar.