Stratum corneum
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{{Infobox Anatomy |
Name = Stratum corneum |
Latin = stratum corneum epidermidis |
GraySubject = 234 |
GrayPage = 1064 |
Image = Skinlayers.png |
Caption = Section of epidermis. (Stratum corneum labeled at top left.) |
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Caption2 = |
System = |
Precursor = |
MeshName = |
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DorlandsPre = s_25 |
DorlandsSuf = 12761112 |
}}
The '''stratum corneum''' ("horny layer") is the outermost layer of the [[epidermis (skin)|epidermis]] (the outermost layer of the [[skin]]). It is composed mainly of dead [[cell (biology)|cell]]s that lack [[cell nucleus|nuclei]]. As these dead cells slough off, they are continuously replaced by new cells from the [[stratum germinativum]] (basale). In the human forearm, for example, about 1300 cells/cm<sup>2</sup>/hr are shed and commonly accumulate as house dust. This outer layer that is sloughed off is also known as the stratum dysjunction.
Cells of the stratum corneum contain [[keratin]], a [[protein]] that helps keep the skin hydrated by preventing [[water]] [[evaporation]]. In addition, these cells can also [[absorption|absorb]] water, further aiding in hydration and explaining why humans and other animals experience [[wrinkle|wrinkling]] of the skin on the [[finger|fingers]] and [[toes]] (colloquially called "pruning") when immersed in water for prolonged periods.
The thickness of the stratum corneum varies according to the amount of protection and/or grip required by a region of the body. For example, the [[hand]]s are typically used to grasp objects, requiring the palms to be covered with a thick stratum corneum. Similarly, the [[sole]] of the [[foot]] is prone to injury, and so it is protected with a thick stratum corneum layer. In general, the stratum corneum contains 15 to 20 layers of dead cells. The stratum corneum has a thickness between 10 and 40 μm. (=0.04mm)
In [[reptile]]s, the stratum corneum is permanent, and is replaced only during times of rapid growth, in a process called [[ecdysis]] or [[moulting]]. The stratum corneum in reptiles contains [[beta-keratin]], which provides a much more-rigid skin layer.
== External links ==
* {{LoyolaMedEd|medicine/dermatology/skinlsn/stcorn.htm}}
* {{BUHistology|08422loa}} - "Integument: thick skin"
{{integumentary_system}}
[[Category:Integumentary system]]
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