Editing Skin condition (section)

== Layer of skin involved ==
{{Main|Integumentary system}}

The skin weighs an average of {{convert|4|kg|lb|abbr=on}}, covers an area of about {{convert|2|m2|sqft|abbr=on}}, and is made of three distinct layers: the [[epidermis (skin)|epidermis]], [[dermis]], and [[subcutaneous tissue]].<ref name="Lookingbill" /> The two main types of human skin are [[glabrous skin]], the nonhairy skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin.<ref name="RooksCD">{{cite book | vauthors = Burns T, Rook A | date = 2006 | title = Rook's Textbook of Dermatology CD-ROM | publisher = Wiley-Blackwell | isbn = 1-4051-3130-6}}</ref> Within the latter type, hairs in structures called [[pilosebaceous unit]]s have a [[hair follicle]], [[sebaceous gland]], and associated [[arrector pili]] muscle.<ref name="Paus">{{cite journal | vauthors = Paus R, Cotsarelis G | title = The biology of hair follicles | journal = The New England Journal of Medicine | volume = 341 | issue = 7 | pages = 491–497 | date = August 1999 | pmid = 10441606 | doi = 10.1056/NEJM199908123410706 }}</ref> [[Embryology|In the embryo]], the epidermis, hair, and glands are from the [[ectoderm]], which is chemically influenced by the underlying [[mesoderm]] that forms the dermis and subcutaneous tissues.<ref name="isbn0-19-261253-0">{{cite book | vauthors = Goldsmith LA |title=Biochemistry and physiology of the skin |publisher=Oxford University Press |year=1983 |isbn=0-19-261253-0 }}</ref><ref name="pmid17314969">{{cite journal | vauthors = Fuchs E | title = Scratching the surface of skin development | journal = Nature | volume = 445 | issue = 7130 | pages = 834–842 | date = February 2007 | pmid = 17314969 | pmc = 2405926 | doi = 10.1038/nature05659 | bibcode = 2007Natur.445..834F }}</ref><ref name="pmid18413712">{{cite journal | vauthors = Fuchs E, Horsley V | title = More than one way to skin . . | journal = Genes & Development | volume = 22 | issue = 8 | pages = 976–985 | date = April 2008 | pmid = 18413712 | pmc = 2732395 | doi = 10.1101/gad.1645908 }}</ref>

=== Epidermis ===
{{Main|Epidermis (skin)}}

The epidermis is the most superficial layer of skin, a [[epithelium|squamous epithelium]] with several [[stratum|strata]]: the [[stratum corneum]], [[stratum lucidum]], [[stratum granulosum]], [[stratum spinosum]], and [[stratum germinativum|stratum basale]].<ref name="Fitz" /> Nourishment is provided to these layers via [[diffusion]] from the dermis, since the epidermis is without direct blood supply.<ref>{{cite web | vauthors = Amirlak B, Shahabi L | veditors = Talavera F, Stadelmann WK, Caputy GG |title=Skin Anatomy|url=http://emedicine.medscape.com/article/1294744-overview|publisher=Medscape|access-date=3 June 2013}}</ref> The epidermis contains four cell types: [[keratinocyte]]s, [[melanocyte]]s, [[Langerhans cell]]s, and [[Merkel cell]]s. Of these, keratinocytes are the major component, constituting roughly 95% of the epidermis.<ref name="RooksCD" /> This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface.<ref name="RooksCD" /> In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.<ref name="bolognia">{{cite book | vauthors = Bolognia JL, Jorizzo JL, Rapini RP |title=Dermatology |publisher=Mosby |location=St. Louis |year=2007 |isbn=978-1-4160-2999-1 }}</ref>

=== Dermis ===
{{Main|Dermis}}

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the [[papillary dermis]] and the [[reticular dermis]].<ref name="Rapini">{{cite book | vauthors = Rapini RP |title=Practical dermatopathology |publisher=Elsevier Mosby |year=2005 |isbn=0-323-01198-5 }}</ref> The superficial papillary dermis [[wikt:interdigitate|interdigitates]] with the overlying [[rete ridge]]s of the epidermis, between which the two layers interact through the basement membrane zone.<ref name="Rapini" /> Structural components of the dermis are [[collagen]], [[elastic fiber]]s, and [[ground substance]] also called extra fibrillar matrix.<ref name="Rapini" /> Within these components are the pilosebaceous units, arrector pili muscles, and the [[eccrine gland|eccrine]] and [[apocrine gland]]s.<ref name="Fitz" /> The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels.<ref name="Fitz" /><ref name="Grant-Kels">{{cite book | vauthors = Grant-Kels JM |title=Color Atlas of Dermatopathology (Dermatology: Clinical & Basic Science) |publisher=Informa Healthcare |year=2007|page=163| isbn=978-0-8493-3794-9 }}</ref> The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.<ref name="LAG">{{cite book | vauthors = Ryan T |chapter=Cutaneous Circulation | veditors = Goldsmith LA |title=Physiology, biochemistry, and molecular biology of the skin |publisher=Oxford University Press |location=New York |edition= 2nd |year=1991 |page=1019 |isbn=0-19-505612-4 }}</ref><ref name="pmid8423379">{{cite journal | vauthors = Swerlick RA, Lawley TJ | title = Role of microvascular endothelial cells in inflammation | journal = The Journal of Investigative Dermatology | volume = 100 | issue = 1 | pages = 111S–115S | date = January 1993 | pmid = 8423379 | doi = 10.1038/jid.1993.33 | doi-access = free }}</ref>

=== Subcutaneous tissue ===
{{Main|Subcutaneous tissue}}

The subcutaneous tissue is a layer of fat between the dermis and underlying [[fascia]].<ref name="Lynch">{{cite book | vauthors = Lynch PJ |title=Dermatology |publisher=Williams & Wilkins |year=1994 |isbn=0-683-05252-7 }}</ref> This tissue may be further divided into two components, the actual fatty layer, or [[panniculus adiposus]], and a deeper vestigial layer of muscle, the [[panniculus carnosus]].<ref name="RooksCD" /> The main cellular component of this tissue is the [[adipocyte]], or fat cell.<ref name="Lynch" /> The structure of this tissue is composed of septal (i.e. linear strands) and [[Lobe (anatomy)|lobular]] compartments, which differ in microscopic appearance.<ref name="Fitz" /> Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.<ref name="Lynch" />