Some body parts have the ability to repair themselves after injury, but others don't repair at all. Once a limb, like an arm or leg, is lost, it can't ever be restored again. In humans, only the wound is healed rather than the body, and scientists have asked themselves why.

In Life Noggin's latest video, "Why Can't Humans Regrow Body Parts?" host Pat Graziosi explains when we lose a limb, our cells close the wound and a blood clot forms, which leads to a scab over the wound, and an eventual scar in the place where the limb used to be. However, we're unable to regrow a body part because the blastema, the bud of a new limb, never grows. Some scientists believe it's because we don't have all the genes necessary to facilitate such a level of regeneration, while other suggest this ability make increase our susceptibility to developing cancers.

Read More: Salamanders' Ability To Regenerate Limbs Offers New Routes For Human Wound Therapy

Unlike humans, salamanders are only vertebrate that can grow its limbs and many other body parts throughout their lifetime. The axolotl, a Mexican salamander, can regenerate almost anything; from their eyes to their spinal cord to event parts of their brain. A scar tissue will never form after an injury, which is a striking difference between their regeneration and a human wound healing.

A salamander's wound closes more rapidly as cells rush to the amputation site. These cells revert back to a less specialized state and begin creating the blastema. As the blastema grows, it begins to form the outline of a new limb and the foot. The cells begin creating new tissues by proliferating and differentiating into things like muscle and bone. The new leg lengthens, filling out the missing segments between the amputation site and the the whole process usually lasts around two months, and then the salamander has a fully regenerated limb.

Scientists propose if humans could regrow their limbs just like salamanders, there still might be an issue. In salamanders, certain jumping genes need to be restrained in their cells, or they might disrupt the regeneration process. Its been discovered proteins within these vertebrates allows them to prevent jumping genes from causing havoc.

The future of limb regeneration in humans is still hopeful. Scientists theorize, because we all evolve from the same place, humans must also have a set of genes that can allow them to grow back new limbs. It's just about trying to uncover how to activate them, or add genes based on the salamander model to create new organs.

Science may some day be able to overcome this human limitation.

See Also:

Fountain-Of-Youth' Gene Accelerates Wound Healing, Hair Regrowth

Stem Cells In Fingernails Are The Key To Regrowing Amputated Finger Tips