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{{chembox
| Verifiedfields = changed
| verifiedrevid = 477226494
| ImageFile = 7-Dehydrocholesterol.svg
| ImageSize = 220
| ImageFile1 = 7-Dehydrocholesterol molecule ball.png
| ImageSize1 = 250
| ImageAlt1 = Ball-and-stick model of 7-dehydrocholesterol
| IUPACName = Cholesta-5,7-dien-3β-ol
| SystematicName = (1''R'',3a''R'',7''S'',9a''R'',9b''S'',11a''R'')-9a,11a-Dimethyl-1-[(2''R'')-6-methylheptan-2-yl]-2,3,3a,6,7,8,9,9a,9b,10,11,11a-dodecahydro-1''H''-cyclopenta[''a'']phenanthren-7-ol
| OtherNames =
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 388534
| InChI = 1/C27H44O/c1-18(2)7-6-8-19(3)23-11-12-24-22-10-9-20-17-21(28)13-15-26(20,4)25(22)14-16-27(23,24)5/h9-10,18-19,21,23-25,28H,6-8,11-17H2,1-5H3/t19-,21+,23-,24+,25+,26+,27-/m1/s1
| InChIKey = UCTLRSWJYQTBFZ-DDPQNLDTBZ
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/C27H44O/c1-18(2)7-6-8-19(3)23-11-12-24-22-10-9-20-17-21(28)13-15-26(20,4)25(22)14-16-27(23,24)5/h9-10,18-19,21,23-25,28H,6-8,11-17H2,1-5H3/t19-,21+,23-,24+,25+,26+,27-/m1/s1-dehydrocholesterol
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = UCTLRSWJYQTBFZ-DDPQNLDTSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 434-16-2
| PubChem = 172
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = BK1IU07GKF
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 17759
| SMILES = O[C@@H]4C/C3=C/C=C1\[C@H](CC[C@]2([C@H]1CC[C@@H]2[C@H](C)CCCC(C)C)C)[C@@]3(C)CC4
| MeSHName = 7-dehydrocholesterol
}}
| Section2 = {{Chembox Properties
| Formula = C27H44O
| MolarMass = 384.638
| Appearance =
| Density =
| MeltingPt =
| BoilingPt =
}}
| Section3 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
}}
[[Image:Skinlayers.png|thumb|250px|right|The epidermal strata of the skin.]]
'''7-Dehydrocholesterol''' ('''7-DHC''') is a [[zoosterol]] that functions in the [[blood plasma|serum]] as a [[cholesterol]] precursor, and is [[photochemically]] converted to [[Cholecalciferol|vitamin D3]] in the [[skin]], therefore functioning as [[provitamin]]-D3. The presence of this compound in human skin enables humans to manufacture vitamin D3 ([[cholecalciferol]]). Upon exposure to [[ultraviolet]] UV-B rays in the sun light, 7-DHC is converted into vitamin D3 via [[Previtamin D3|previtamin D3]] as an intermediate [[isomer]]. It is also found in the [[milk]] of several mammalian species. [[Lanolin]], a waxy substance that is naturally secreted by wool-bearing mammals, contains 7-DHC which is converted into vitamin D by sunlight and then ingested during grooming as a nutrient. In insects 7-dehydrocholesterol is a precursor for the hormone [[ecdysone]], required for reaching adulthood. It was discovered by Nobel-laureate organic chemist [[Adolf Windaus]].

==Biosynthesis==
It is synthesized from [[lathosterol]] by the enzyme [[lathosterol oxidase]] (lathosterol 5-desaturase). This is the next-to-last step of cholesterol biosynthesis. Defective synthesis results in the human inherited disorder [[lathosterolosis]] resembling [[Smith–Lemli–Opitz syndrome]]. Mice where this gene has been deleted lose the ability to increase vitamin D3 in the blood following UV exposure of the skin.

==Location ==
The skin consists of two primary layers: an inner layer, the [[dermis]], comprising largely [[connective tissue]], and an outer, thinner [[Epidermis (skin)|epidermis]]. The thickness of the epidermis ranges from 0.08 mm to greater than 0.6 mm (from 0.003 to 0.024 inches). The epidermis comprises 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. The production of pre-vitamin D3 is, therefore, greatest in these two layers.

==Radiation==
Synthesis of pre-vitamin D3 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 295 and 300 [[nanometer|nm]] and, thus, the production of vitamin D3 will occur primarily at those wavelengths. The two most important factors that govern the generation of pre-vitamin D3 are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol deep in the stratum basale and stratum spinosum. Light-emitting diodes ([[LED]]s) can be used to produce the radiation.

Another important consideration is the quantity of 7-dehydrocholesterol present in the skin. Under normal circumstances, ample quantities of 7-dehydrocholesterol (about 25–50 [[microgram|μg]]/cm2 of skin) are available in the [[stratum spinosum]] and [[stratum basale]] of human skin to meet the body's vitamin D requirements. 7-DHC insufficiency has been proposed as an alternate cause for Vitamin D deficiency.

== Sources ==
7-DHC can be produced by animals and plants via different pathways. It is not produced by fungi in significant amounts. It is made by some [[algae]], but the pathway is poorly understood. It can also be produced by some bacteria.

Industrially, 7-DHC generally comes from [[lanolin]], and is used to produce vitamin D3 by UV exposure. [[Lichen]] ([[Cladonia rangiferina]]) is used to produce [[vegan]] D3.

7-DHC is used for vitamin D3 synthesis via [[lanosterol]] in land animals, via [[cycloartenol]] in plants, and in algae together with another provitamin D [[ergosterol]] for D2. In fungi solely ergosterol is used for synthesis of D2 via lanosterol.

==Interactive pathway map==
{{VitaminDSynthesis_WP1531|highlight=7-Dehydrocholesterol}}

== See also ==
* [[Vitamin D]]
* [[Smith–Lemli–Opitz syndrome]]
* [[7-Dehydrocholesterol reductase]]

{{Vitamin}}
{{Cholesterol metabolism intermediates}}
{{Vitamin D receptor modulators}}

{{二次利用|date=9 December 2023}}
{{DEFAULTSORT:Dehydrocholesterol, 7-}}
[[Category:Cholestanes]]
[[Category:Sterols]]
[[Category:Nutrition]]
[[Category:Vitamin D]]

7-Dehydrocholesterol/en - Revision history

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