Because our skin is the part of us that confronts our world directly, it is also quite likely to be damaged frequently. It has to have a method for repair. Because it is made up of epidermis and dermis, both highly regenerative tissues, it is quite capable of much repair... but there is a limit.
Recovery after damage in general:
Think about the epidermis for starters...
What part of the epidermis allows for regeneration? I hope you are now thinking about the stratum basale. All the cell division to replenish the epidermis occurs in the stratum basale. And this epidermal layer is also the one that picks up the most nutrients from the underlying dermal blood vessels. I have drawn an extremely simplified schematic of epidermis in the figure below in part A. It is so simplified that not all the layers are included, and I just wrote "etc." to remind you that more layers are needed on top. I also only drew the nuclei in the cells of the stratum basale, so that this layer would stand out.
If you are cut very lightly, so that just the epidermis is affected (and then you don't even bleed), the cells in the stratum basale can easily divide and repair the damage. This is shown in part B of the figure below. In this figure, the stratum basale is unaffected, so it can just keep dividing and recreate the layers above it to return the epidermis to the "normal" condition shown in part A.
However, if the cut is deeper, and cuts through the entire epidermis, the repair is more difficult. First of all, you will bleed and a scab will form in the cut. Secondly, if the two ends of the cut are at all separate, as shown in part C of the above figure, the stratum basale has to divide to re-grow and fill up the space between the ends. After this is complete, regrowth of the entire epidermis is simple-- all that is needed is more cell division of the cells in the stratum basale.
Now, you should understand why, when you have a large cut, it is necessary to get stitches, to sew the two ends back together. After stitches, the stratum basale doesn't have to grow too much laterally before it encounters the other side of the cut... then it can focus on re-growing the more apical layers of the epidermis so that you will heal fully and faster. Also, the stratum basale can only reform completely if it has something on which to grow! It has to be able to find good dermis to sit on and to make a new basement membrane with. If the ends are sewn back together, the dermis will recover faster as well.
Now think about the dermis...
The dermis is also highly regenerative. Why? Because its fibroblasts are numerous and can re-secrete the matrix fibers as well as divide to make more fibroblasts. Fibroblasts are also quite mobile, and can move into the damaged area so that they will re-establish the dermis where it needs it. Macrophages can also crawl around and clean up the scab material, so that it gets cleared away as it is no longer needed to maintain the continuity of the skin.
I would like you to consider burns separately, because they tend to be less discrete than cuts. A cut can be localized to a certain place, but burns can be much more extensive across the skin area. The healing process from a burn, as far as the epidermis and dermis regeneration goes, is similar. But if you receive large burns, your recovery and treatment will differ.
Besides cell division, what else is going on in skin during regeneration?
Figure 6.14 in your book is excellent in showing the steps skin takes to recovery. Any cut or burn that gets into the dermis leads to bleeding. Blood that flows outside of a blood vessel will clot (as you will learn in more detail next semester) and form a scab. The scab prevents further blood loss and inhibits infections from entering the body. As cells in your skin divide and attempt to repair the damage, the clot will have to be removed. Macrophages invade and remove scab material as is needed to enable tissue recovery. Follow this process in this figure in your book!
© 2011 STCC Foundation Press