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How does regeneration work in animals?

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Quick answer

Regeneration in animals happens when cells near a wound dedifferentiate into a blastema, a cluster of unspecialised cells. These cells multiply and then specialise into the missing tissues, rebuilding the lost part. Salamanders regrow limbs, starfish regrow arms, and planarians regrow whole bodies, but humans mostly form scar tissue instead.

Regeneration works when specialised cells at a wound site dedifferentiate into a mass called a blastema, then multiply and reorganise into the missing body parts. The extent of regrowth depends on the animal: some replace whole limbs, while humans mostly repair tissue with scar.

Step by step

  1. An injury or amputation triggers an immediate response: cells near the wound site begin to divide and migrate.
  2. These cells dedifferentiate, losing their specialised features, and form a mass called a blastema.
  3. The blastema cells receive chemical signals that tell them their position and what structures to build.
  4. The cells proliferate, increasing in number to provide enough material for the new part.
  5. The cells then differentiate into the required cell types—skin, muscle, bone, nerve—and arrange into the correct pattern.
  6. The new structure grows and integrates with existing tissues, completing the regeneration.

Key things to understand

  1. When a body part is lost, cells near the wound site migrate to form a blastema, a cluster of unspecialised, dividing cells.
  2. These blastema cells are guided by chemical signals and positional memory that tell them what structures to rebuild.
  3. The cells then differentiate into the needed tissues—skin, muscle, bone, nerve—and arrange themselves into the correct shape.
  4. Animals such as salamanders and starfish regenerate whole limbs or arms, while planarians can regrow an entire body from a fragment.
  5. Mammals, including humans, have limited regeneration: the liver can regrow, but limbs are replaced by scar tissue instead.

Labelled diagram

  1. Amputation

    The limb is severed, and a wound epidermis forms over the stump.

  2. Blastema

    Cells dedifferentiate and accumulate under the wound epidermis.

  3. Growth

    Blastema cells divide rapidly, building a bulge called a regeneration bud.

  4. Pattern formation

    Cells differentiate and arrange into bone, muscle, and skin.

  5. New limb

    A fully functional limb replaces the lost one.

How a salamander regrows a limb

Real-world examples

  • A salamander can regrow a severed leg, including bones, muscles, and nerves, within weeks.
  • A starfish can regenerate a lost arm, and some species can regrow an entire body from a single arm.
  • Planarians, flatworms cut into pieces, can regrow complete worms from each fragment.
  • The human liver can regenerate up to two-thirds of its mass after partial removal, though it does not regrow limbs.

Common mistake

✗ Myth: Humans can regenerate entire limbs just like salamanders.

✓ Fact: Humans cannot regrow limbs; our wounds heal with scar tissue. We do have limited regeneration, such as the liver regrowing after partial removal, but complex structures like arms do not regenerate.

People also ask

What animals can regenerate body parts?
Many animals can regenerate body parts. Salamanders and newts regrow limbs, tails, and even parts of their heart and eyes. Starfish regrow arms, and some can regrow a whole body from one arm. Planarians regrow entire bodies from small pieces. Zebrafish can regenerate fins and heart tissue. Among mammals, the deer regrows its antlers, and the spiny mouse can regenerate skin without scarring.
How do planarians regenerate?
Planarians regenerate using a large population of adult stem cells called neoblasts. When a planarian is cut, neoblasts migrate to the wound site, divide, and form a blastema. They then differentiate into all the needed cell types, guided by positional signals. A small fragment can regrow a complete worm, including a new brain and digestive system, within about two weeks.
Why can't humans regenerate limbs?
Humans cannot regenerate limbs because our cells respond to injury by forming scar tissue, which blocks the blastema-like process. Our immune system quickly sends cells that deposit collagen, sealing the wound. Also, human cells have limited ability to dedifferentiate into the needed stem-cell state. Research on regeneration aims to understand and possibly overcome these barriers.
Can humans regrow limbs like salamanders?
No, humans cannot regrow limbs. Our wounds heal by forming scar tissue, which blocks the blastema-like process. We can regenerate some tissues, such as the liver and the lining of the gut, but not complex structures like arms or legs.
What is a blastema?
A blastema is a mass of unspecialised cells that forms at the site of an amputation in regenerating animals. These cells divide and later specialise to rebuild the missing part. It acts like a temporary building crew for the new limb.
Why do some animals regenerate better than others?
Regeneration ability depends on how well an animal's cells can dedifferentiate and how its immune system responds. Animals like salamanders have cells that easily revert to a stem-cell-like state, while mammals tend to form scar tissue quickly, which stops regrowth.
Do starfish really regrow arms?
Yes, starfish can regrow lost arms. If an arm is cut off, the starfish grows a new one from the stump. Some species can even regenerate an entire body from a single arm if part of the central disc is attached.

Part of the guide: Nature & Earth: Living Things and Rocks →