Remarkable Regeneration: From Invertebrates to Humans

Throughout the lifespan of an organism, it is possible for certain parts to become damaged or lost. Most organisms possess the ability to replace these defective or missing parts, a phenomenon referred to as regeneration.

Regeneration in Animals

The capacity for regeneration is observed in various animals, both invertebrates and vertebrates.

Invertebrates

Sponges: Sponges can regenerate their entire body from a conglomeration of their cells.

Regeneration In Planarian 

Hydra: Similar to sponges, hydra also possesses this regenerative ability.

When a Planarian worm is severed, regeneration initiates at each cut surface, resulting in the formation of a blastema. Cell division and differentiation continue within the blastema until a sufficient number of replacement cells are generated. Consequently, two complete worms are formed from the original one.

Earthworm: The earthworm can regenerate the first four or five segments of its head and even longer sections of its tail. If one of its large pincer claws is lost, it begins to regrow. In the case of a sea star, new arms are formed if one or more of its existing arms are removed.

Vertebrates

Among vertebrate animals, the most remarkable regenerative capacity discovered thus far exists in tailed amphibians such as newts and salamanders, which can fully regenerate their limbs when they are lost.

Adult frogs do not exhibit any regenerative ability; only their larvae possess the capacity to regenerate lost limbs.

Although most lizards can regenerate their tails, they are unable to regenerate entire organs. However, they can regenerate tissues, thereby repairing damaged or missing parts.

Regeneration in Humans

In humans, examples of regeneration include the healing of skin wounds, bone regeneration, and blood replacement. Organs such as the tongue, liver, and pancreas demonstrate extensive regenerative capabilities after being damaged.

The ratio between nerve cell processes and those of limbs plays a critical role in regeneration. For instance, in salamanders, if nerves leading to a limb are severed before amputation, regeneration does not occur. Conversely, if an additional nerve is surgically implanted at the base of a frog's leg, regeneration can take place.