We have skin that covers our bodies but when does it stop being skin? Our tongues have skin but do our throats? What about our stomachs, lungs, intestines, and everything on the inside they don’t have skin. So where does it end and become whatever it is?
In: Biology
I think what you are asking is where are the transitions to “insides”. At all of your openings your epithelial tissue transitions from “ cutaneous” or skin which has hair, sweat and oil glands etc, to “mucus membranes” which among other things secrete mucus to protect the body from pathogens. Your lips are the most obvious of the transition zones. Notice how they are smoother, heal differently, and have different textures than your chin, but then notice another change even from the top of your lip to the inside of your mouth.
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