Editing Skin (section)

===Epidermis===
{{main|Epidermis}}

The epidermis is composed of the outermost layers of the skin. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing [[pathogens]] from entering, and is a stratified squamous [[epithelium]],<ref name="Rooks">{{cite book
 | last1=McGrath |first1=J.A. |last2=Eady|first2=R.A. |last3=Pope|first3=F.M.
 | title=Rook's Textbook of Dermatology
 | year=2004 | edition=7th
 | publisher=Blackwell Publishing | isbn=978-0-632-06429-8
 | pages=3.1–3.6
}}</ref> composed of [[cell division|proliferating]] basal and [[cell differentiation|differentiated]] suprabasal [[keratinocyte]]s.

[[Keratinocyte]]s are the major [[cell (biology)|cells]], constituting 95% of the [[epidermis (skin)|epidermis]],<ref name="Rooks" /> while [[Merkel cell]]s,  [[melanocyte]]s and [[Langerhans cell]]s are also present. The [[epidermis (skin)|epidermis]] can be further subdivided into the following ''strata'' or layers (beginning with the outermost layer):<ref>{{cite book|url=https://openstax.org/details/books/anatomy-and-physiology-2e |title=Anatomy and Physiology 2e |publisher=OpenStax |page=164 |last1=Betts |first1=J. Gordon |display-authors=etal |year=2022 |isbn=978-1-711494-06-7}}</ref>
* [[Stratum corneum]]
* [[Stratum lucidum]] (only in [[Hand#Human anatomy|palms]] and [[sole (foot)|soles]])
* [[Stratum granulosum]]
* [[Stratum spinosum]]
* [[Stratum basale]] (also called the ''stratum germinativum'')
[[Keratinocyte]]s in the [[stratum basale]] proliferate through [[mitosis]] and the daughter [[cell (biology)|cells]] move up the strata changing shape and composition as they undergo multiple stages of [[cell differentiation]] to eventually become anucleated. During that process, [[keratinocyte]]s will become highly organized, forming [[cell junction|cellular junctions]] ([[desmosomes]]) between each other and secreting [[keratin]] [[proteins]] and [[lipids]] which contribute to the formation of an [[extracellular matrix]] and provide mechanical [[strength of materials|strength]] to the skin.<ref name="Pmid">{{cite journal | pmid=19333614 | year=2009 | last1=Breitkreutz | first1=D | last2=Mirancea | first2=N | last3=Nischt | first3=R | title=Basement membranes in skin: Unique matrix structures with diverse functions? | volume=132 | issue=1 | pages=1–10 | doi=10.1007/s00418-009-0586-0 | journal=Histochemistry and Cell Biology| s2cid=21633122 }}</ref> [[Keratinocyte]]s from the [[stratum corneum]] are eventually shed from the surface ([[desquamation]]).

The [[epidermis (skin)|epidermis]] contains no [[blood vessel]]s, and [[cell (biology)|cells]] in the deepest layers are nourished by diffusion from [[blood]] [[capillaries]] extending to the upper layers of the [[dermis]].