Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Epidermis
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
{{short description|Outermost of the three layers that make up the skin}} {{about|skin in mammals}} {{Infobox microanatomy | Name = Epidermis | Latin = epidermis | Image = Epidermis-delimited.JPG | Caption = [[Histology|Microscopic]] image of the epidermis, which constitutes the outer layer of skin, shown here by the white bar | Image2 = Epidermal layers.png | Caption2 = Microscopic image showing the layers of the epidermis. The ''stratum corneum'' appears more compact in this image than above because of different sample preparation. | Precursor = | System = [[Integumentary system]] | PartOf = [[Skin]] }} The '''epidermis''' is the outermost of the three layers that comprise the [[skin]], the inner layers being the [[dermis]] and [[Subcutaneous tissue|hypodermis]].<ref>{{Cite book|title=Wheater's functional histology a text and colour atlas| vauthors = Young B |publisher=Elsevier|year=2014|isbn=9780702047473|pages=160 & 175}}</ref> The epidermal layer provides a barrier to [[infection]] from environmental [[pathogens]]<ref name="Lookingbill">{{cite book | vauthors = Marks JG, Miller J | title = Lookingbill and Marks' Principles of Dermatology | edition = 4th | publisher = Elsevier | year = 2006 | pages = 1–7 | isbn = 978-1-4160-3185-7 }}</ref> and regulates the amount of water released from the body into the [[atmosphere]] through [[transepidermal water loss]].<ref name="Proksch">{{cite journal | vauthors = Proksch E, Brandner JM, Jensen JM | title = The skin: an indispensable barrier | journal = Experimental Dermatology | volume = 17 | issue = 12 | pages = 1063–1072 | date = December 2008 | pmid = 19043850 | doi = 10.1111/j.1600-0625.2008.00786.x | s2cid = 31353914 }}</ref> The epidermis is composed of [[stratified squamous epithelium|multiple layers of flattened cells]]<ref name="Rooks">{{cite book | vauthors = McGrath JA, Eady RA, Pope FM | 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> that overlie a base layer ([[stratum basale]]) composed of [[Epithelium#Cell types|columnar cells]] arranged perpendicularly. The layers of cells develop from [[stem cell]]s in the basal layer. The thickness of the epidermis varies from 31.2μm for the [[penis]] to 596.6μm for the [[Sole (foot)|sole of the foot]] with most being roughly 90μm. Thickness does not vary between the sexes but becomes thinner with age.<ref name="Lintzeri Karimian Blume‐Peytavi Kottner 2022 pp. 1191–1200">{{cite journal |last1=Lintzeri |first1=D.A. |last2=Karimian |first2=N. |last3=Blume-Peytavi |first3=U. |last4=Kottner |first4=J. |date=2022 |title=Epidermal thickness in healthy humans: a systematic review and meta-analysis |journal=Journal of the European Academy of Dermatology and Venereology |volume=36 |issue=8 |pages=1191–1200 |doi=10.1111/jdv.18123 |issn=0926-9959|doi-access=free |pmid=35366353 }}</ref> The human epidermis is an example of [[epithelium]], particularly a [[stratified squamous epithelium]]. The word epidermis is derived through Latin {{ety|grc|epidermis}}, itself {{ety|grc|epi|over, upon}} and {{ety|grc|derma|skin}}. Something related to or part of the epidermis is termed epidermal. == Structure == ===Cellular components=== The epidermis primarily consists of [[keratinocytes]]<ref name="Rooks" /> ([[cell proliferation|proliferating]] basal and [[cell differentiation|differentiated]] suprabasal), which comprise 90% of its cells, but also contains [[melanocyte]]s, [[Langerhans cell]]s, [[Merkel cell]]s,<ref name="Andrews"/>{{rp|2–3}} and inflammatory cells. Epidermal thickenings called [[Rete pegs|Rete ridges]] (or rete pegs) extend downward between [[dermal papillae]].<ref>[http://medical-dictionary.thefreedictionary.com/rete+ridge TheFreeDictionary > rete ridge] Citing: The American Heritage Medical Dictionary Copyright 2007, 2004</ref> [[Blood]] [[capillaries]] are found beneath the epidermis, and are linked to an [[arteriole]] and a [[venule]]. The epidermis itself has no [[circulatory system|blood supply]] and is nourished almost exclusively by diffused oxygen from the surrounding air.<ref name=stucker>{{cite journal | vauthors = Stücker M, Struk A, Altmeyer P, Herde M, Baumgärtl H, Lübbers DW | title = The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis | journal = The Journal of Physiology | volume = 538 | issue = Pt 3 | pages = 985–994 | date = February 2002 | pmid = 11826181 | pmc = 2290093 | doi = 10.1113/jphysiol.2001.013067 }}</ref> Cellular mechanisms for regulating [[water]] and [[sodium]] levels ([[Epithelial sodium channel|ENaC]]s) are found in all layers of the epidermis.<ref name="2017-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Boggula VR, Vaknine H, Sharma S, Kleyman T, Hanukoglu A | title = Expression of epithelial sodium channel (ENaC) and CFTR in the human epidermis and epidermal appendages | journal = Histochemistry and Cell Biology | volume = 147 | issue = 6 | pages = 733–748 | date = June 2017 | pmid = 28130590 | doi = 10.1007/s00418-016-1535-3 | s2cid = 8504408 | url = https://zenodo.org/record/890756 }}</ref> ===Cell boundaries=== Epidermal cells are tightly interconnected to serve as a tight barrier against the exterior environment. The junctions between the epidermal cells are of the [[adherens junction]] type, formed by transmembrane proteins called [[cadherins]]. Inside the cell, the cadherins are linked to [[actin]] filaments. In immunofluorescence microscopy, the actin filament network appears as a thick border surrounding the cells,<ref name="2017-Hanukoglu" /> although the [[microfilament|actin filaments]] are actually located inside the cell and run parallel to the cell membrane. Because of the proximity of the neighboring cells and tightness of the junctions, the actin [[immunofluorescence]] appears as a border between cells.<ref name="2017-Hanukoglu" /> ===Layers=== [[File:Skinlayers.png|thumb|Schematic image showing a section of epidermis, with epidermal layers labeled]] The epidermis is composed of four or five layers, depending on the skin region.<ref>{{cite book|url=https://openstax.org/details/books/anatomy-and-physiology-2e |title=Anatomy and Physiology | edition = 2nd |publisher=OpenStax |page=164 | vauthors = Betts JG |display-authors=etal |year=2022 |isbn=978-1-711494-06-7}}</ref> Those layers from outermost to innermost are:<ref name="Lookingbill" /> ; [[Keratin#Cornification|cornified layer]] (''[[stratum corneum]]''): [[File:Confocal image of the stratum corneum.jpg|thumb|Confocal image of the stratum corneum]]Composed of 10 to 30 layers of polyhedral, anucleated [[corneocyte]]s (final step of keratinocyte [[cell differentiation|differentiation]]), with the palms and soles having the most layers. Corneocytes contain a [[protein]] envelope (cornified envelope proteins) underneath the plasma membrane, are filled with water-retaining [[keratin]] proteins, attached together through [[desmosome|corneodesmosomes]] and surrounded in the [[extracellular]] space by stacked layers of [[lipids]].<ref name="bensouillah">{{cite web|title=Skin structure and function|url=http://www.radcliffe-oxford.com/books/samplechapter/7750/01_bensouillah-241a6c80rdz.pdf|url-status=dead|archive-url=https://web.archive.org/web/20101214062704/http://www.radcliffe-oxford.com/books/samplechapter/7750/01_bensouillah-241a6c80rdz.pdf|archive-date=2010-12-14|access-date=2015-01-07}}</ref> Most of the barrier functions of the epidermis localize to this layer.<ref name="elias">{{cite journal | vauthors = Elias PM | title = The skin barrier as an innate immune element | journal = Seminars in Immunopathology | volume = 29 | issue = 1 | pages = 3–14 | date = April 2007 | pmid = 17621950 | doi = 10.1007/s00281-007-0060-9 | s2cid = 20311780 }}</ref> ; clear/translucent layer (''[[stratum lucidum]]'', only in palms and soles): This narrow layer is found only on the palms and soles. The epidermis of these two areas is known as "thick skin" because with this extra layer, the skin has 5 epidermal layers instead of 4. ; granular layer (''[[stratum granulosum]]''): [[File:Confocal image of the stratum granulosum.jpg|thumb|Confocal image of the stratum granulosum]]Keratinocytes lose their [[cell nucleus|nuclei]] and their [[cytoplasm]] appears granular. Lipids, contained into those keratinocytes within [[lamellar bodies]], are released into the extracellular space through [[exocytosis]] to form a lipid barrier that prevents water loss from the body as well as entry of foreign substances. Those polar lipids are then converted into non-polar lipids and arranged parallel to the cell surface. For example [[glycosphingolipids]] become [[ceramides]] and [[phospholipids]] become [[free fatty acids]].<ref name="bensouillah" /> ; spinous layer (''[[stratum spinosum]]''): [[File:Confocal image of the stratum spinosum with some basal cell clusters.jpg|thumb|Confocal image of the stratum spinosum already showing some clusters of basal cells]]Keratinocytes become connected through [[desmosomes]] and produce lamellar bodies, from within the [[golgi apparatus|Golgi]], enriched in polar lipids, [[glycosphingolipids]], free [[sterols]], [[phospholipids]] and catabolic enzymes.<ref name="Proksch" /> Langerhans cells, immunologically active cells, are located in the middle of this layer.<ref name="bensouillah" /> ; basal/germinal layer (''[[stratum germinativum|stratum basale/germinativum]]''): [[File:Confocal image of the stratum basale showing some papillae.jpg|thumb|Confocal image of the stratum basale already showing some papillae]]Composed mainly of proliferating and non-proliferating keratinocytes, attached to the [[basement membrane]] by [[hemidesmosomes]]. [[Melanocyte]]s are present, connected to numerous keratinocytes in this and other strata through [[dendrites]]. [[Merkel cells]] are also found in the [[stratum basale]] with large numbers in touch-sensitive sites such as the [[fingertip]]s and [[lip]]s. They are closely associated with cutaneous [[nerves]] and seem to be involved in light touch sensation.<ref name="bensouillah" /> ; [[Malpighian layer]] (''stratum malpighii''): This is usually defined as both the [[stratum basale]] and [[stratum spinosum]].<ref name="Rooks" /> The epidermis is separated from the dermis, its underlying [[tissue (biology)|tissue]], by a [[basement membrane]]. ===Cellular kinetics=== ====Cell division==== As a [[stratified squamous epithelium]], the epidermis is maintained by [[cell division]] within the stratum basale. [[cell differentiation|Differentiating]] cells delaminate from the [[basement membrane]] and are displaced outward through the epidermal layers, undergoing multiple stages of differentiation until, in the stratum corneum, losing their nucleus and fusing to squamous sheets, which are eventually shed from the surface ([[desquamation]]). Differentiated keratinocytes secrete keratin proteins, which contribute to the formation of an [[extracellular matrix]] that is an integral part of the skin barrier function. In normal skin, the rate of keratinocyte production equals the rate of loss,<ref name="Rooks" /> taking about two weeks for a cell to journey from the stratum basale to the top of the stratum granulosum, and an additional four weeks to cross the stratum corneum.<ref name="Lookingbill" /> The entire epidermis is replaced by new cell [[cell division|growth]] over a period of about 48 days.<ref name="Iizuka">{{cite journal | vauthors = Iizuka H | title = Epidermal turnover time | journal = Journal of Dermatological Science | volume = 8 | issue = 3 | pages = 215–217 | date = December 1994 | pmid = 7865480 | doi = 10.1016/0923-1811(94)90057-4 }}</ref> ====Calcium concentration==== Keratinocyte differentiation throughout the epidermis is in part mediated by a [[calcium]] gradient, increasing from the stratum basale until the outer stratum granulosum, where it reaches its maximum, and decreasing in the stratum corneum. Calcium concentration in the stratum corneum is very low in part because those relatively dry cells are not able to dissolve the ions.<ref>{{Cite journal |last=Bikle |first=Daniel D. |last2=Xie |first2=Zhongjian |last3=Tu |first3=Chia-Ling |date=July 2012 |title=Calcium regulation of keratinocyte differentiation |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC3491811/ |journal=Expert Review of Endocrinology & Metabolism |volume=7 |issue=4 |pages=461–472 |doi=10.1586/eem.12.34 |issn=1744-6651 |pmc=3491811 |pmid=23144648}}</ref> This calcium gradient parallels keratinocyte differentiation and as such is considered a key regulator in the formation of the epidermal layers.<ref name="Proksch" /> Elevation of extracellular calcium concentrations induces an increase in [[intracellular]] free calcium concentrations.<ref>{{cite journal | vauthors = Hennings H, Kruszewski FH, Yuspa SH, Tucker RW | title = Intracellular calcium alterations in response to increased external calcium in normal and neoplastic keratinocytes | journal = Carcinogenesis | volume = 10 | issue = 4 | pages = 777–780 | date = April 1989 | pmid = 2702726 | doi = 10.1093/carcin/10.4.777 }}</ref> Part of that intracellular increase comes from calcium released from intracellular stores<ref>{{cite journal | vauthors = Pillai S, Bikle DD | title = Role of intracellular-free calcium in the cornified envelope formation of keratinocytes: differences in the mode of action of extracellular calcium and 1,25 dihydroxyvitamin D3 | journal = Journal of Cellular Physiology | volume = 146 | issue = 1 | pages = 94–100 | date = January 1991 | pmid = 1990023 | doi = 10.1002/jcp.1041460113 | s2cid = 21264605 }}</ref> and another part comes from transmembrane calcium influx,<ref>{{cite journal | vauthors = Reiss M, Lipsey LR, Zhou ZL | title = Extracellular calcium-dependent regulation of transmembrane calcium fluxes in murine keratinocytes | journal = Journal of Cellular Physiology | volume = 147 | issue = 2 | pages = 281–291 | date = May 1991 | pmid = 1645742 | doi = 10.1002/jcp.1041470213 | s2cid = 25858560 }}</ref> through both calcium-sensitive [[chloride channels]]<ref>{{cite journal | vauthors = Mauro TM, Pappone PA, Isseroff RR | title = Extracellular calcium affects the membrane currents of cultured human keratinocytes | journal = Journal of Cellular Physiology | volume = 143 | issue = 1 | pages = 13–20 | date = April 1990 | pmid = 1690740 | doi = 10.1002/jcp.1041430103 | s2cid = 8072916 }}</ref> and voltage-independent cation channels permeable to calcium.<ref>{{cite journal | vauthors = Mauro TM, Isseroff RR, Lasarow R, Pappone PA | title = Ion channels are linked to differentiation in keratinocytes | journal = The Journal of Membrane Biology | volume = 132 | issue = 3 | pages = 201–209 | date = March 1993 | pmid = 7684087 | doi = 10.1007/BF00235738 | s2cid = 13063458 }}</ref> Moreover, it has been suggested that an extracellular calcium-sensing [[cell surface receptor|receptor]] (CaSR) also contributes to the rise in intracellular calcium concentration.<ref>{{cite journal | vauthors = Tu CL, Oda Y, Bikle DD | title = Effects of a calcium receptor activator on the cellular response to calcium in human keratinocytes | journal = The Journal of Investigative Dermatology | volume = 113 | issue = 3 | pages = 340–345 | date = September 1999 | pmid = 10469331 | doi = 10.1046/j.1523-1747.1999.00698.x | doi-access = free }}</ref> ===Development=== Epidermal [[organogenesis]], the formation of the epidermis, begins in the cells covering the [[embryo]] after [[neurulation]], the formation of the [[central nervous system]]. In most [[vertebrates]], this original one-layered structure quickly transforms into a two-layered [[tissue (biology)|tissue]]; a temporary outer layer, the embryonic ''periderm'', which is disposed once the inner [[basal layer]] or ''[[stratum germinativum]]'' has formed.<ref name="Gilbert-2003">{{cite book | title = Developmental Biology | chapter = The Epidermis and the Origin of Cutaneous Structures | vauthors = Gilbert SF | chapter-url = https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=dbio&part=A2929 | publisher = Sinauer Associates | year = 2000 | isbn = 978-0-87893-243-6 | url-access = registration | url = https://archive.org/details/developmentalbio00gilb }}</ref> This inner layer is a [[germ layer|germinal epithelium]] that gives rise to all epidermal cells. It divides to form the outer [[spinous layer]] (''[[stratum spinosum]]''). The cells of these two layers, together called the [[Malpighian layer]](s) after [[Marcello Malpighi]], divide to form the superficial [[granularity|granular]] layer (''Stratum granulosum'') of the epidermis.<ref name="Gilbert-2003" /> The cells in the stratum granulosum do not divide, but instead form skin cells called keratinocytes from the [[granule (cell biology)|granule]]s of [[keratin]]. These skin cells finally become the [[cornified layer]] (''stratum corneum''), the outermost epidermal layer, where the cells become flattened sacks with their nuclei located at one end of the cell. After [[birth]] these outermost cells are replaced by new cells from the stratum granulosum and throughout [[life]] they are shed at a rate of 30 – 90 milligrams of skin flakes every hour, or 0.720 - 2.16 grams per day.<ref>{{cite journal | vauthors = Weschler CJ, Langer S, Fischer A, Bekö G, Toftum J, Clausen G | title = Squalene and cholesterol in dust from danish homes and daycare centers | journal = Environmental Science & Technology | volume = 45 | issue = 9 | pages = 3872–3879 | date = May 2011 | pmid = 21476540 | doi = 10.1021/es103894r | bibcode = 2011EnST...45.3872W | s2cid = 1468347 | url = https://backend.orbit.dtu.dk/ws/files/5602736/plugin-es103894r.pdf }}</ref> Epidermal [[developmental biology|development]] is a product of several [[growth factor]]s, two of which are:<ref name="Gilbert-2003" /> * [[Transforming growth factor]] Alpha ([[TGFα]]) is an [[autocrine]] growth factor by which basal cells stimulate their own [[cell division|division]]. * [[Keratinocyte growth factor]] (KGF or [[FGF7]]) is a [[paracrine]] growth factor produced by the underlying [[dermis|dermal]] [[fibroblast]]s in which the [[cell proliferation|proliferation]] of basal cells is regulated. == Function == ===Barrier=== The epidermis serves as a barrier to protect the body against [[microbial]] pathogens, [[oxidant stress]] ([[UV light]]), and [[chemical]] compounds, and provides [[mechanics|mechanical]] resistance to minor injury. Most of this barrier role is played by the stratum corneum.<ref name="elias" /> ;Characteristics * Physical barrier: Epidermal keratinocytes are tightly linked by [[cell junctions|cell–cell junctions]] associated to [[cytoskeletal]] proteins, giving the epidermis its mechanical strength.<ref name="Proksch" /> * Chemical barrier: Highly organized lipids, acids, hydrolytic [[enzymes]], and [[antimicrobial peptides]]<ref name="Proksch" /> inhibit passage of external chemicals and pathogens into the body. * Immunologically active barrier: The [[humoral]] and [[cellular immunity|cellular]] constituents of the [[immune system]]<ref name="Proksch" /> found in the epidermis actively combat infection. * Water content of the [[stratum corneum]] drops towards the surface, creating hostile conditions for pathogenic [[microorganism]] growth.<ref name="elias" /> * An acidic [[pH]] (around 5.0) and low amounts of water make the epidermis hostile to many microorganic pathogens.<ref name="elias" /> * Non-pathogenic microorganisms on the surface of the epidermis help defend against pathogens by competing for [[food]], limiting its availability, and producing chemical [[secretions]] that inhibit the growth of pathogenic microbiota.<ref name="elias" /> ;Permeability * [[Psychological]] [[stress (psychological)|stress]], through an increase in [[glucocorticoids]], compromises the stratum corneum and thus the barrier function.<ref>{{cite journal | vauthors = Denda M, Tsuchiya T, Elias PM, Feingold KR | title = Stress alters cutaneous permeability barrier homeostasis | journal = American Journal of Physiology. Regulatory, Integrative and Comparative Physiology | volume = 278 | issue = 2 | pages = R367–R372 | date = February 2000 | pmid = 10666137 | doi = 10.1152/ajpregu.2000.278.2.R367 | s2cid = 558526 }}</ref> * Sudden and large shifts in [[humidity]] alter stratum corneum [[tissue hydration|hydration]] in a way that could allow entry of pathogenic microorganisms.<ref>{{cite journal | vauthors = Tsai JC, Guy RH, Thornfeldt CR, Gao WN, Feingold KR, Elias PM | title = Metabolic approaches to enhance transdermal drug delivery. 1. Effect of lipid synthesis inhibitors | journal = Journal of Pharmaceutical Sciences | volume = 85 | issue = 6 | pages = 643–648 | date = June 1996 | pmid = 8773963 | doi = 10.1021/js950219p }}</ref> ===Skin hydration=== The ability of the skin to hold water is primarily due to the [[stratum corneum]] and is critical for maintaining [[healthy]] skin.<ref>{{cite journal | vauthors = Blank IH | title = Factors which influence the water content of the stratum corneum | journal = The Journal of Investigative Dermatology | volume = 18 | issue = 6 | pages = 433–440 | date = June 1952 | pmid = 14938659 | doi = 10.1038/jid.1952.52 | doi-access = free }}</ref> Skin hydration is quantified using [[corneometry]].<ref name="pmid2459872">{{cite journal | vauthors = Blichmann CW, Serup J | title = Assessment of skin moisture. Measurement of electrical conductance, capacitance and transepidermal water loss | journal = Acta Dermato-venereologica | volume = 68 | issue = 4 | pages = 284–90 | date = 1988 | pmid = 2459872 | doi = 10.2340/0001555568284290 | doi-broken-date = 1 November 2024 }}</ref> Lipids arranged through a [[gradient]] and in an organized manner between the cells of the stratum corneum form a barrier to [[transepidermal water loss]].<ref>{{cite journal | vauthors = Downing DT, Stewart ME, Wertz PW, Colton SW, Abraham W, Strauss JS | title = Skin lipids: an update | journal = The Journal of Investigative Dermatology | volume = 88 | issue = 3 Suppl | pages = 2s–6s | date = March 1987 | pmid = 2950180 | doi = 10.1111/1523-1747.ep12468850 }}</ref><ref>{{cite journal | vauthors = Bonté F, Saunois A, Pinguet P, Meybeck A | title = Existence of a lipid gradient in the upper stratum corneum and its possible biological significance | journal = Archives of Dermatological Research | volume = 289 | issue = 2 | pages = 78–82 | date = January 1997 | pmid = 9049040 | doi = 10.1007/s004030050158 | s2cid = 10787600 }}</ref> ===Skin color=== The amount and distribution of [[melanin]] [[pigment]] in the epidermis is the main reason for variation in [[skin color]] in ''[[Homo sapiens]]''. Melanin is found in the small [[melanosome]]s, particles formed in melanocytes from where they are transferred to the surrounding keratinocytes. The size, number, and arrangement of the melanosomes vary between racial groups, but while the number of melanocytes can vary between different body regions, their numbers remain the same in individual body regions in all human beings. In white and Asian skin the melanosomes are packed in "aggregates", but in black skin they are larger and distributed more evenly. The number of melanosomes in the keratinocytes increases with [[UV radiation]] exposure, while their distribution remain largely unaffected.<ref>{{cite book | title = Black skin: structure and function | vauthors = Montagna W, Prota G, Kenney JA | author-link1 = William Montagna | publisher = Gulf Professional Publishing | year = 1993 | isbn = 978-0-12-505260-3 | url = https://books.google.com/books?id=BpL8V2YJkQ4C&pg=PA69 | page = 69 }}</ref> ===Touch=== The skin contains specialized epidermal touch receptor cells called [[Merkel cells]]. Historically, the role of Merkel cells in sensing touch has been thought to be indirect, due their close association with nerve endings. However, recent work in mice and other model organisms demonstrates that Merkel cells intrinsically transform touch into electrical signals that are transmitted to the nervous system.<ref>{{cite journal | vauthors = Moehring F, Halder P, Seal RP, Stucky CL | title = Uncovering the Cells and Circuits of Touch in Normal and Pathological Settings | journal = Neuron | volume = 100 | issue = 2 | pages = 349–360 | date = October 2018 | pmid = 30359601 | pmc = 6708582 | doi = 10.1016/j.neuron.2018.10.019 }}</ref> ==Clinical significance== {{for|a comprehensive list|List of cutaneous conditions}} [[Laboratory]] culture of keratinocytes to form a 3D structure ([[artificial skin]]) recapitulating most of the properties of the epidermis is routinely used as a tool for [[drug]] development and testing. ===Hyperplasia=== Epidermal [[hyperplasia]] (thickening resulting from [[cell proliferation]]) has various forms: * '''Acanthosis''' is diffuse [[Epidermis (skin)|epidermal]] [[hyperplasia]] (thickening of the skin, and not to be confused with [[acanthocyte]]s).<ref name="Kumar">{{cite book | vauthors = Kumar V, Fausto N, Abbas A | date = 2004 | title = Robbins & Cotran Pathologic Basis of Disease | edition = 7th | publisher = Saunders | page = 1230 | isbn = 0-7216-0187-1}}</ref> It implies increased thickness of the [[Malpighian layer]] ([[stratum basale]] and [[stratum spinosum]]).<ref>{{cite web|url=http://www.healthcare.uiowa.edu/dermatology/dpt/Acanthosis.htm |title=Acanthosis | vauthors = Stone MS, Ray TL |date=September 1995 |work=DermPathTutor |publisher=Department of Dermatology, University of Iowa |access-date=17 May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120529202432/http://www.healthcare.uiowa.edu/dermatology/dpt/Acanthosis.htm |archive-date=29 May 2012 }}</ref> [[Acanthosis nigricans]] is a black, poorly defined, velvety [[hyperpigmentation|hyperpigmented]] acanthosis, usually observed in the back of neck, axilla, and other folded regions of the skin. * '''[[Focal epithelial hyperplasia]]''' (Heck's disease) is an asymptomatic, benign neoplastic condition characterized by multiple white to pinkish [[papule]]s that occur diffusely in the oral cavity.<ref>{{cite journal | vauthors = Tenore G, Palaia G, Del Vecchio A, Galanakis A, Romeo U | title = Focal epithelial hyperplasia (Heck's disease) | journal = Annali di Stomatologia | volume = 4 | issue = Suppl 2 | pages = 43 | date = 2013-10-24 | pmid = 24353818 | pmc = 3860189 }}</ref><ref name="Andrews">{{cite book | vauthors = James WD, Berger TG, Elston DM, Aydemir EH, Odom RB |title=Andrews' Diseases of the Skin: clinical Dermatology |publisher=Saunders Elsevier |year=2006 |isbn=0-7216-2921-0 }}</ref>{{rp|411}} * '''Pseudoepitheliomatous hyperplasia''' (PEH) is a benign condition characterized by hyperplasia of the epidermis and epithelium of [[skin appendage]]s,<ref name="ChakrabartiChakrabarti2014"/> with irregular squamous strands extending down into the dermis,<ref name="Lynch2004">{{cite journal| vauthors = Lynch JM |title=Understanding Pseudoepitheliomatous Hyperplasia|journal=Pathology Case Reviews|volume=9|issue=2|year=2004|pages=36–45|issn=1082-9784|doi=10.1097/01.pcr.0000117275.18471.5f|s2cid=71497554}}</ref> and closely simulating squamous cell carcinoma (SCC).<ref name="ChakrabartiChakrabarti2014">{{cite journal | vauthors = Chakrabarti S, Chakrabarti PR, Agrawal D, Somanath S | title = Pseudoepitheliomatous hyperplasia: a clinical entity mistaken for squamous cell carcinoma | journal = Journal of Cutaneous and Aesthetic Surgery | volume = 7 | issue = 4 | pages = 232–234 | year = 2014 | pmid = 25722605 | pmc = 4338470 | doi = 10.4103/0974-2077.150787 | doi-access = free }}</ref> <gallery> File:Acanthosis-nigricans4.jpg|[[Acanthosis nigricans]] File:Hecks disease.jpg|[[Heck's disease]] File:Histopathology of pseudoepitheliomatous hyperplasia, low magnification.jpg|Pseudoepitheliomatous hyperplasia (PEH), low magnification, with acanthotic squamous epithelium with irregular thick finger-like downgrowths into the underlying dermis. File:Histopathology of pseudoepitheliomatous hyperplasia, high magnification.jpg|PEH, high magnification, with reactive-appearing squamous downgrowths with no significant cytologic atypia. </gallery> In contrast, [[hyperkeratosis]] is a thickening of the [[stratum corneum]], and is not necessarily due to hyperplasia. ==Additional images== {{gallery | height = 150 | width = 150 |Image:Normal Epidermis and Dermis with Intradermal Nevus 10x.JPG|Epidermis and dermis of human skin |Image:Skin.png|Cross-section of all skin layers |File:Blausen 0353 Epidermis.png|Illustration of epidermal layers |Image:HautFingerspitzeOCT.gif|[[Optical coherence tomography]] of fingertip }} == See also == * [[List of distinct cell types in the adult human body]] * [[Skin repair]] == References == {{Reflist|colwidth=30em}} {{integumentary system}} {{Authority control}} {{DEFAULTSORT:Epidermis (Skin)}} [[Category:Skin anatomy]]
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)
Pages transcluded onto the current version of this page
(
help
)
:
Template:About
(
edit
)
Template:Authority control
(
edit
)
Template:Cite book
(
edit
)
Template:Cite journal
(
edit
)
Template:Cite web
(
edit
)
Template:Ety
(
edit
)
Template:For
(
edit
)
Template:Gallery
(
edit
)
Template:Infobox microanatomy
(
edit
)
Template:Integumentary system
(
edit
)
Template:Reflist
(
edit
)
Template:Rp
(
edit
)
Template:Short description
(
edit
)