Regeneration

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domesticated om

Stickler for details
Valued Senior Member
I'm sitting at my cubicle today bored, and I was inspired to ponder the subject of regeneration while looking at a cut on my finger.

About a week or so ago, I was using an apple corer. I accidently gouged a humongous chunk of flesh out of my thumb when I tried to push the little apple core cylinder through the hole in the middle.
Since then, I've gone through a ton of bandaids, and two days ago, I got tired of having to constantly re-wrap my thumb, so I gave up.

At any rate- so I've been given this opportunity to watch my cut heal itself on a daily basis. The original cut was deep enough that it peeled away a large flap of skin, and effectively eliminated part of my finger print. Well- as the healing progresses, I notice the underlying layer of skin growing a replacement ---which includes the section of missing fingerprint.

I think to myself "why is it that the human body can replace a fingerprint, and can not replace an entire arm?" I mean- in order to grow a new fingerprint, the adjacent cells would need to be equpped with some sort of blueprint that tells them what the finished product is supposed to look like -- right? Besides the obvious differennce (complicated array of cells vs simpler array of cells) what's stopping the human body with a severed arm from rebuilding a new arm? The blueprint is obviously there.

BTW--- I'm obviously not even close to being an expert in biology, but I love to learn new things, and retain alot of what I'm told. That being said, thanks in advance for any info.
 
Mammal skin has two major layers - the epidermis and the dermis - and each are subdivided into multiple layers. Had your cut eliminated a large section of the entire lower dermis, then it would not regrow with fingerprint. The dermis layer genetically influences the epidermis and will reconstruct it by a process known as "embryonic induction" that determines the specific structure, even though it does not physically contribute to the rebuild of the epidermal cells. The dermis influences the function (hair follicles, sweat glands, etc.), shape and form of the overlying epidermis, but does not contribute to its healing or reduplication except through a genetic influence that is not completely understood.
 
I think to myself "why is it that the human body can replace a fingerprint, and can not replace an entire arm?"
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You're getting ahead of yourself. The body can't even replace deeper layers of skin and nerve. Observe burn victims, who require skin grafts.
 
I'm basically reparaphrasing what I learned in class and what is written in our 2005 copyright text in Comparative Anatomy.

I recently was hospitalized and underwent two months of rehabilitation because of 2nd and 3rd degree burns over 10% of my body that destroyed the upper epidermis level, causing escar coverage formation. Any other deeper burns (4th, 5th, 6th degree) cause burning of the underlying muscle and bone. Because of the commendable intensive care that I received, you can hardly see a scar.
 
The body can't even replace deeper layers of skin and nerve
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That's not the point. The question was WHY can't it, not whether it could or not. It obviously can't.

As for the answer to the question I really don't know, but I do know that some salamanders (axotls or something like that?) CAN re-grow entire arms. Not that their arms are very big, and I'm guessing that's partly why it can... maybe evolutionarily speaking it's too much of a waste of time for "higher" (I truly hate using "higher" and "lower" but I can't think of any other word I could use) vertebrates to try to re-grow arms and stuff. If a "higher" vertebrate looses an arm or something, it will most likely die anyway. And even if it can live, it probably can't feed itself very well so using the little energy it can get to re-grow that arm would be a wase.

or maybe I'm completely wrong... I don't really think it was actively selected against, since an armless vertebrate probably couldn't even mate. Maybe the lack of ability to re-grow an arm just comes about because we can't re-grow deeper layers of skin and nerve... because... well, I'm just gonna shut up because I'm not really saying anything... I ramble too much :-S
 
TheAlphaWolf:
That's not the point. The question was WHY can't it, not whether it could or not. It obviously can't.
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I just think it's a little silly to ask 'Why can't we replace an arm!' when we can't even replace deep layers of skin! :p
 
genetic codominance, but as I stated above (page before) it is not yet totally explained.
 
mountainhare said:
TheAlphaWolf:

I just think it's a little silly to ask 'Why can't we replace an arm!' when we can't even replace deep layers of skin! :p
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stem cell research
 
Again, Wikipedia comes through, but read on below it:

"Regeneration is a common feature in invertebrates, but far more limited in most vertebrates. Nevertheless, even humans possess some degree of regeneration ability. Children under 6 years of age are capable of regenerating lost fingertips and the human liver retains its ability to regenerate throughout a person's lifetime.

Aside from being used to generally describe any number of specific healing processes, regeneration also is a specific method of healing that is noted for its ability to regrow lost limbs, severed nerve connections, and other wounds. This is present in some animals such as the newt, hydra, and a type of mouse. If the processes behind regeneration are fully understood, it is believed this would lead to better treatment for individuals with nerve injuries, broken backs, paralysis, and missing limbs....

In salamanders the regeneration process begins immediately after amputation. After amputation, epidermis covers the stump within 24 hours, forming a structure called the apical epidermal crest (AEC). This results in the formation of a blastema (or a layer of dedifferentiated cells). At the same time, pattern formation genes – such as HoxA and HoxD – are activated as they were when the limb was formed in the embryo. Distal structures such as toes form first from the blastema. Intermediate layers are filled in afterwards. Motor neurons grow with the regenerated limb, and innervate the same target muscles they originally controlled. The entire process takes around three months in the adult and then the limb becomes fully functional.
http://en.wikipedia.org/wiki/Regeneration_(biology)

"Mice Regrow Hearts

Scientists have created "miracle mice" that can regenerate amputated limbs or damaged vital organs, making them able to recover from injuries that would kill or permanently disable normal animals. The experimental animals are unique among mammals in their ability to regrow their heart, toes, joints and tail. And when cells from the test mouse are injected into ordinary mice, they too acquire the ability to regenerate, the US-based researchers say.

Their discoveries raise the prospect that humans could one day be given the ability to regenerate lost or damaged organs, opening up a new era in medicine. The research leader, Ellen Heber-Katz, professor of immunology at the Wistar Institute, a US biomedical research centre, said the ability of the mice at her laboratory to regenerate organs appeared to be controlled by about a dozen genes. She is still researching the genes' exact functions, but it seems almost certain humans have comparable genes. "We have experimented with amputating or damaging several different organs, such as the heart, toes, tail and ears, and just watched them regrow," she said. "It is quite remarkable. The only organ that did not grow back was the brain.
http://www.worldhealth.net/p/its-a-miracle---mice-regrow-hearts-2005-09-16.html
 
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