7-Dehydrocholesterol
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Ruziklan
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[[:en:User:NicoV/Wikipedia Cleaner/Documentation|WikiCleaner]] 0.75 - Repairing link to disambiguation page - [[Wikipedia:Disambiguation pages with links|You can help!]]
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| ImageFile = 7-Dehydrochlolesterol.png
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| Section1 = {{Chembox Identifiers
| CASNo = 434-16-2
| PubChem = 172
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| MeSHName = 7-dehydrocholesterol
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| Section2 = {{Chembox Properties
| Formula = C<sub>27</sub>H<sub>44</sub>O
| MolarMass = 384.638
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| Section3 = {{Chembox Hazards
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[[Image:Skinlayers.png|thumb|250px|right|The epidermal strata of the skin.]]
'''7-Dehydrocholesterol''' is a [[zoosterol]] that functions in the [[blood plasma|serum]] as a [[cholesterol]] precursor, and is converted to pre-[[Cholecalciferol|vitamin D<sub>3</sub>]] in the [[skin]], therefore functioning as [[provitamin]]-D<sub>3</sub>. The presence of this compound in human skin enables humans to manufacture [[Cholecalciferol|vitamin D<sub>3</sub>]] from [[ultraviolet|ultra-violet]] rays in the sun light, via an intermediate [[isomer]] pre-vitamin D<sub>3</sub>. It is also found in the [[milk]] of several mammalian species.<ref>"7-dehydrocholesterol." The American Heritage Stedman's Medical Dictionary. Houghton Mifflin Company, 2002. 21 Jan. 2007. [http://www.answers.com/topic/7-dehydrocholesterol Answers.com].</ref> It was discovered by Nobel-laureate organic chemist [[Adolf Windaus]].
==Location ==
The skin consists of two primary layers: the inner layer called the [[dermis]], composed largely of [[connective tissue]], and the outer thinner [[Epidermis (skin)|epidermis]]. The thickness of the epidermis ranges from 0.08[[millimetre|mm]] to more than 0.6mm (0.003 to 0.024 inches).<ref> Frediric Martini et al. (2006). Human Anatomy. Pearson/Benjamin-Cummings Publishers, p. 89. ISBN:0-8053-7211-3.</ref> The epidermis consists of five ''strata''; from outer to inner they are: the [[stratum corneum]], [[stratum lucidum]], [[stratum granulosum]], [[stratum spinosum]], and [[stratum basale]]. The highest concentrations of 7-dehydrocholesterol are found in the epidermal layer of skin, specifically in the stratum basale and stratum spinosum.<ref name= Norman> Norman, Anthony W. (1998) [http://www.ajcn.org/cgi/reprint/67/6/1108.pdf Sunlight, season, skin pigmentation, vitamin D, and 25-hydroxyvitamin D:integral components of the vitamin D endocrine system.] Am J Clin Nutr;67:1108–10.</ref> The production of pre-vitamin D<sub>3</sub> is therefore greatest in these two layers, whereas production in the other layers is reduced.
==Radiation==
Synthesis of pre-vitamin D<sub>3</sub> in the skin involves [[UVB radiation]] which effectively penetrates only the epidermal layers of skin. 7-Dehydrocholesterol absorbs UV light most effectively at [[wavelength]]s between 270–290 [[nanometer|nm]] and thus the production of vitamin D<sub>3</sub> will only occur at those wavelengths. The two most important factors that govern the generation of pre-vitamin D<sub>3</sub> are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol deep in the stratum basale and stratum spinosum.<ref name= Norman/> Another important consideration is the quantity of 7-dehydrocholesterol present in the skin. Under normal circumstances, ample quantities of 7-dehydrocholesterol (about 25–50 [[milligram|mg]]/[[Centimetre|cm]]<sup>2</sup> of skin) are available in the stratum spinosum and stratum basale of human skin to meet the body's vitamin D requirements.
==See also==
* [[Vitamin D]]
* [[Smith-Lemli-Opitz syndrome]]
* [[7-Dehydrocholesterol reductase]]
==References==
<references/>
==External links==
[[Category:Sterols]]
[[Category:Nutrition|Dehydrocholesterol, 7-]]
[[de:7-Dehydrocholesterol]]
[[ja:7-デヒドロコレステロール]]
[[pl:7-dehydrocholesterol]]