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If the squamous (top) layer of epidermis, or skin, is burned or damaged in another way, will it then be replaced by the next layer of below?

Also, from where does the basal membrane originate? Does it regenerate from a different layer of cells?

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    $\begingroup$ I edited your question so people might find it easier to answer. hope that's okay - feel free to re-edit. $\endgroup$ – shigeta May 23 '14 at 17:12
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The epidermis is a four- or five-layered epithelium. The top layers are squamous whereas the bottom ones are more columnar (http://en.wikipedia.org/wiki/Epidermis_(skin)). The lowest layer is separated from the dermis by the basal membrane (a.k.a. basal lamina, basement membrane).

The process of wound healing in skin is extremely complex and obviously depends on the individual wound and how many layers are destroyed. There is a lot of detail on Wikipedia: http://en.wikipedia.org/wiki/Wound_healing.

If the basement membrane is not disrupted, there are two main components as a rule of thumb: 1) outwards-inwards migration, i.e. cells surrounding a wound will migrate into the wound. 2) bottom-upwards differentiation, i.e. the bottom-most layer contains replicating cells which will differentiate and squamify to regenerate upper layers.

Something like this (picture modified from Wikipedia): enter image description here

If the wound is bleeding, this means the basement membrane is disrupted and the dermis underneath is also wounded (the epidermis itself contains no blood vessels). In this case, the dermis needs to regenerate first, in a process which is probably similar as described above. Simultaneously, the bottom-most epidermal cell layer will proliferate to close the gap, and then deposit new basement membrane. Remember that the basement membrane is a mesh of proteins, not an actual cell layer.

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It would first be good to look at the different layers within the skin as you mentioned in your question.

The skin is made up of:

  • Epidermis: the outermost layer of skin, provides a waterproof barrier and creates our skin tone
  • Dermis: beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands
  • Hypodermis: deeper subcutaneous tissue is made of fat and connective tissue

enter image description here

Different kinds of damage can occur to the skin, including burns, which have different degrees based on what layer of skin is damaged and how far down the burn goes. Therefore, it is not as simple as the epidermis itself getting burned, it could also be much worse and the healing process may be hindered if too much damage occurs.

Burns can happen when the skin is exposed to heat (from fire or hot liquids), electricity, corrosive chemicals, or radiation (UV rays from the sun or tanning beds, or radiation treatments).

Burns are classified as follows, according to the severity of tissue damage:

  • First degree burns: affect only the outer layer of the skin (epidermis), causing pain and redness. The prototype is mild sunburn
  • Second degree burns: extend to the second layer of the skin (the dermis), causing pain, redness, and blisters that may ooze; deep second degree burns may progress to third degree burns over the course of several days
  • Third degree burns: involve both layers of the skin and may also damage the underlying bones, muscles, and tendons; the burn site appears pale, charred, or leathery; there is generally no pain in the area because the nerve endings are destroyed.
  • Fourth degree burns: extend through the skin and subcutaneous fat into the underlying muscle and bone; are stiff and charred

Depending on the type of burn, different skin generation occurs. If it is a really terrible burn, then a skin graft from another area of the body may be needed, as it cannot regenerate the epidermis layer due to the excessive damage.

First degree burns are the easiest from which to recover [...] the dermis remains intact and can support the regeneration of the epidermis. It may happen that the skin will get inflamed (due to responses in the underlying dermis) during this time; the inflammation is to encourage clean-up cells (macrophages) and nutrients to reach the damaged area.

It appears as though the dermis itself will help with the regeneration of the epidermal cells.

In a second degree burn, the dermis is also affected, at least partially. But, with a second-degree burn, most (or at least some) skin accessory organs typically remain in tact. Remember, these accessory organs (like glands and hairs) are built from invaginations of the epidermis, creating the epithelium of the glands or hair follicles. If these organs survive the burn, the epithelial cells that remain will begin to divide to regenerate a new epidermis.

Third-degree burns are the worst. In these, even the accessory organs are destroyed. How can we recover from this? Skin grafts are about the best way, but they cannot really be done across one's entire body, so a very widespread third-degree burn is not usually something that a person can recover from.

AND although this is a separate question and topic, the basal membrane is thought to be of epithelial origin, but this is very complex and still not completely known. There is more information about it in this article; Cellular origin of the dermal-epidermal basement membrane (Marinkovich et al. 1993). It is a dated article but has some interesting information.

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The Basal Membrane is regenerated by a different layer of cells. Not replaced by the skin layer below if your epidermis and squamous was shed and the skin below would replace it that layer would soon shed and after a while your skin would have been shed down to your muscle! If you want to do a small experiment to see what happens to your epidermis when it is broken try biting the skin of the end of your fingers, Then see what happends.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

  • $\begingroup$ U haven't answered the last two questions, from where does the basal membrane originate and does it regenerate from a different layer of cells. $\endgroup$ – The Last Word May 27 '14 at 6:56

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