– where does skin in your body stop being skin? Is the roof of the mouth skin? The back of the throat? How does skin attach and transition to non-skin flesh?
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The vermilion border of the lips marks the transition between “outside skin” and “inside skin”
The term for internal “skin” is mucous membrane. It has different qualities. The inside of your anus, inside of mouth, etc. is mucous membrane.
It doesnt really.. your whole digestion system is kinda outside your skin, but inside your body. Humans are giant donuts with badly shaped holes starting in our mouths and ending in our anus
humans, which are like the Eukaryotic single cell organisms from which we evolved, are just complex donuts. our entire digestive system is technically on the outside of our bodies, with skin and epithelial tissue forming a continuous donut meat sac.
You are epithelial cells all the way through your digestive tract and your skin is what I think I remember learning in biology
I always used to think about this with the gel-filled squishy tube toys from arcade. I googled them and they’re marketed as “water wiggle squishy toys”. That’s our body. A continuous membrane filled with fluid with two puckered ends.
Wait till he hears that the “skin” around his lips is pretty much the same “skin” as around his arse hole.
You essentially have two types of „skin“.
TLDR: in short you inner skin (mucosa) and outer skin (dermis) are fundamentally the same. Both have a connective tissue that holds it together and a layer above that protects it. Skin hardens and has nerve endings, whereas mucosa secretes slime and often doesnt have nerve endings. The transitions are in lips, eyelids, genitals, anus.
One is what we would normally refer to as skin, everything that covers your outside. The outer layer is called Epidermis, which roughly translates to outer skin. The top part is essentially dead cells that hardened to a degree and server as a shield. The part underneath replenishes these cells as they fall off iver time. The dermis is the next layer containing the hair, blood vessels, nerve endings, etc. it mostly consist out of connective tissue, giving the skin its elasticity.
The Mucosa is your internal skin. It‘s quite similar to regular skin, but a bit different. The top layer is called epithelial cells. Where skin builds a layer of dead cells for protection , mucosa secretes a slimy substance. Under that is the lamina propria, which is similar to the dermis. Its the underlying connective tissue that also has blood vessels, etc.
The junction between those two is called mucocutaneous junction. These are the areas where skin transitions to mucosa. In humans those areas are lips, nostrils, conjuntivae (inside part of the eyelids), urethra, vagina, foreskin and anus.
And now onto why we are this way:
Evolution started off as single cells. Over time those single cells became more complex and complex. Eventually they were too large to become even larger for the most part. So some cells attaches to one another, forming colonies.
The first large colonies where little balls of cells with a hollow inside. At some point however they folded in. Like you pushed your finger into a soft ball. Now this ball has two layers, the one facing outside and the one facing inside, as well as an opening.
This colony became more and more complex. Eventually the inside layer became less protective, using slime to keep itself safe. Its purpose was processing the food. The outside layer became harder and more resilient. This happened in countless different ways.
This pattern exists until today. The inner and outter skin are fairly similar but adapted to different features.
Don’t know, but what I do know is that the skin inside your cheek is the same kind of skin as inside a vagina! So there’s that fun fact for ya.
please see this interesting excerpt i found [here](https://www3.nd.edu/~jsapirst/textbook/chapter_29.html) when googling this to figure out the best way to explain it:
> The internal structures of the body are entirely covered by a continuous layer of epithelial tissue. The part of this layer which is in contact with the outside environment is called the skin; those parts of it that lie within the body (and are yet outside it) are the mucus membranes.
>This idea of a structure being both inside and outside may be confusing, and it may help to consider the body as a long doughnut, the skin and mucus membranes corresponding to the outside of the doughnut and the internal structures being encased between them. The part of the doughnut which is around the hole corresponds to the mucus membranes, the rest to the skin.
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