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Very simple: Why (and how) is regenerated skin different from original ?

As we know we lose skin cells that becomes the dust in out homes and it always grows back to full thickness right ? So when I have a cut, I imagined it to heal provisionally with whatever possible and then after some time to replace itself with the normal skin that is coded in my chromosomes. So why doesn't it do that ? Scars remain and the color is always different from the neighbor parts.

Update:

  • Why we get scars?
  • What about skin transplants ?
  • Why doesn't skin actually grow/replace itself?

Update 2:

  • (I've been thinking) Skin has lots of different layers, right ? So when an area is damaged does it regenerate all layers or just one for being simple and efficient (in "hope" the subject will take precautions not to damage this part of body again, so that regenerating everything back to 100% would be overkill) ?
  • I'm not a scientist, I have only the basics from school, so I'll probably not understand most of the technical terms
  • also I'm more interested about an explanation that goes towards the "survival of the fittest" rule, and not so much about the biochemical reactions in our bodies (because it was just some random mutation that turned out to be the better choice for us → why?)
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    $\begingroup$ This is a very large topic regarding wound healing (en.wikipedia.org/wiki/Wound_healing) and the scaring is primarily caused by inflammatory factors, which are important in initiating wound healing response, leading to a trade of! $\endgroup$
    – Behzad Rowshanravan
    Aug 1, 2014 at 10:12
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    $\begingroup$ There are other reasons for scars.. If the underlying collagen fibers are damaged then the new ones dont get incorporated in the exact same orientation.. You dont get scars that easily.. You can also refer any book on clinical anatomy.. $\endgroup$
    – WYSIWYG
    Aug 1, 2014 at 11:33
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    $\begingroup$ Is that a lie scientist are telling us ?... What sort of a statement is this? Scientists don't lie, governments and profiteers do. $\endgroup$
    – WYSIWYG
    Aug 1, 2014 at 11:35
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    $\begingroup$ @Leck.. 1. you are not supposed to attach your social assumptions when asking a scientific question. 2. This site is not your school classroom where the TA is supposed to teach you. If something is already there in wikipedia then why are you asking it- why dont you simply read it from there. If you can't understand what is written there then ask your professor or a friend. Though it is allowed here to ask something that you don't understand but all that is expected is that you make an effort. Nobody is obliged to teach you. $\endgroup$
    – WYSIWYG
    Aug 1, 2014 at 11:49
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    $\begingroup$ @WYSIWYG You've been rude here. I was reading this before I commented (AND I answered the "I wonder why" by myself if you read what's in the brackets). And I also can't see the close votes because I'm too low on rep (don't really care). If I find no answer here then I'll keep it as one of those life's mysteries that make my life worthwhile. Bye! $\endgroup$
    – Leck
    Aug 1, 2014 at 12:04

2 Answers 2

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Human skin is made up of three layers [1]:

  1. Epidermis; it contains no blood vessels; it has 5 cellular layers (starting from surface):
    • stratum corneum
    • stratum lucidum
    • stratum granulosum
    • stratum spinosum
    • stratum germinativum
  2. Dermis; it is separated from the above by the basal membrane; made up of connective tissue (with blood vessels and nerve endings)
  3. Hypodermis - it is not even considered part of the skin

Gray940.png
"Gray940". Licensed under Public domain via Wikimedia Commons.

Why (and how) is regenerated skin different from original ?

Why? Skin is a very important organ. It protects from pathogens, it maintains body temperature, it keeps body water [1], etc. How? That depends on what causes the regeneration. I've emphasized two terms in the above list.

  • Stratum corneum represents the "skin cells that becomes the dust in our homes and it always grows back to full thickness". It is lost during a physiological process called desquamation [2]. The cells that are lost are non living corneocytes. Their only purpose is to from a protection barrier [3].
  • Basement membrane holds the germinativum layer of the epidermis. Injuries that do not affect it are repaired by complete regeneration of all destroyed layers. However, if the injury destroys membrane continuity, the germinative cells on the edges will fail to "reconnect" with each other, thus the layers derived from them will follow the same rule. A process of fibrosis is triggered. The result of extensive fibrosis is a scar, containing collagen secreted by the granulation tissue with dermal origins. Yet, the germinative layer tends to join back together [6], but probably the excess collagen production, without the limiting basement membrane, bulges into the epidermis and limits germinative layer extension. That's why keeping the edges of the tissue close to each other reduces excessive fibrosis and allows germinative layer regeneration, thus resulting in none to small, barely visible scars.

How deep should an injury be in order not to affect basement membrane? No more than 0.06 to 0.08 mm [5].

What about skin transplants ?

Skin grafts contain at least a part of dermis [4], which will allow granulation tissue formation thus permitting revascularisation and making the graft stick. Otherwise it would fall off and/or be lost by necrosis.

References:

  1. Wikipedia contributors, "Skin," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Skin&oldid=619454074 (accessed August 4, 2014).
  2. Wikipedia contributors, "Desquamation," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Desquamation&oldid=614028888 (accessed August 4, 2014).
  3. Wikipedia contributors, "Stratum corneum," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Stratum_corneum&oldid=615247326 (accessed August 4, 2014).
  4. Wikipedia contributors, "Skin grafting," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Skin_grafting&oldid=603324006 (accessed August 4, 2014).
  5. Sandby-Møller J, Poulsen T, Wulf HC. Epidermal thickness at different body sites: relationship to age, gender, pigmentation, blood content, skin type and smoking habits. Acta Derm. Venereol. 2003;83(6):410-3. doi: 10.1080/00015550310015419. PubMed PMID: 14690333.
  6. Dawn A. Tamarkin, Ph.D. Repair of skin. 2011 STCC Foundation Press. Available from http://faculty.stcc.edu/AandP/AP/AP1pages/Units1to4/skin/repairof.htm (accessed 04.08.2014)
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You're confusing an emergent system with a determined system. Your cells have programming which emerges as the form you see. You are using determinism to decide what your form should be. Determinism gives one reaction for every action. Biology is emergent, not deterministic. The biological mechanisms which are responsible for healing exist in a different information space, with different evolutionary pressures from those which generated your form. The close approximation of scar tissue to undamaged flesh is an emergent property of these two instructions sharing the same physical location. There is no communication between the information which patterned your form and the information which heals your body.

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  • $\begingroup$ This is a good explinaion $\endgroup$
    – user1357
    Aug 2, 2014 at 18:49
  • $\begingroup$ I don't understand q_q. Or explain the information space you're referencing. Are chromosomes the deterministic information space ? What is the "different information space" ? $\endgroup$
    – Leck
    Aug 4, 2014 at 8:01
  • $\begingroup$ Genes are the buildings blocks of biological information. Different genes are selected for and against and the fact that you can differentially regulate them is what separates them into their own information space. What you look like comes in large part from hox genes which have very different evolutionary pressures from genes regulating collagen production during healing. $\endgroup$
    – 12345678910111213
    Oct 30, 2015 at 7:02

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