Is it always scar tissue and it just blends in better or does the body sometimes grow skin?
In: Biology
Think of it like this. You live in a brick house. Your living room has a great big wall to the street with a big window and fancy door. Unfortunately you have no pictures or blueprints of this wall. If you knock out a brick or two, and hire a contractor to fix the hole, he will be able to fix the missing bricks quite easily just by assuming that there used to be bricks where the hole is. Now, a car runs through your great big front wall and completely destroys it. You hire a contractor again. Now remember, this contractor is forced to work completely under assumption. When looking at the missing wall, he assumes that it was a brick wall, because that’s what the rest of the house is. He rebuilds a brick wall, and it is hardly discernible from the other 3 walls. What he failed to rebuild was the great big window and the fancy door, because there was no indication that those were there before just from looking at the walls around it. Now think of your skin as the house and your body as the contractor. It is extremely good at using its best guess to rebuild something (usually) pretty well, but sometimes the damage is just too much for your body to handle without external help (transplants, etc.)
Some animals regrow whole body parts, but somewhere in our ancestry, the adaptation of scarring provided a survival benefit (faster and less resource-intensive healing) and we’ve been stuck with it ever since. The mechanisms for regrowth still exist, and sometimes they do work in limited ways (IIRC kids can regrow lost fingertips, for instance), and there’s research into how they can be activated for bigger injuries.
Human skin has layers. When the bottom most layer (the basal cell layer) is damaged, scar tissue forms. The basal layer produces new skin cells. If that layer is damaged, that area can no longer produce skin cells, so scar tissue fills in the gap. More superficial wounds that don’t damage the basal layer are less likely to scar.
On top of what other people have said, it also has to do with the gene expression patterns of cells in the tissue. When our skin is formed, stem cells are able to divide and differentiate into many cell lines and that gives the skin its appearance and functionality. As we develop and age, those stem cells are gone and we are not able anymore to just make more skin. Scar tissue is made of “dumber” cells that can do the job of keeping the integrity of the skin and not much more.
Plants are a very good example of how sometimes scar tissue is the answer, and sometimes new tissue. If you nick in the stem, scar tissue will appear, but if a root is broken, the plant is able to produce a new root. Plants are awesome.
Also some types of cancer/tumors are basically cells that behave like stem cells, generating new tissue and differentiated cells but in an erratic way. Check out “teratome” in google Images if you want to see a blob with hair and teeth. xD
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