Pro-D Synthesis Lab Report

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Endogenous synthesis of vitamin D takes place in two steps. In first step the ultraviolet (UV-B) spectrum (wave length 290-360 nm) impinges on human skin and facilitates the conversion of 7-dehydrocholesterol present in the plasma membrane of the cells in upper skin layers, mainly in the stratum basale and the stratum spinosum to pro vitamin D3. UV light B breaks the B ring of 7-dehydrocholesterol to form a pre D isomer26-27. In second step the Pro vitamin D3 which is inherently unstable rapidly isomerizes to D3 in a thermo sensitive but non catalytic process. With continued exposure of UV-B, Pro- D3 is converted to biologically inactive lumisterol . Tachysterol is also formed but like pro-D3 it does not accumulate with extended UV radiations24,28. The formation of lumisterol and tachysterol is reversible and can be converted back to pre-D3 as pre-D3 levels fall. Thus prolonged …show more content…

The other hand, vitamin D2 and vitamin D3 derived from supplements, fortified foods and fish ingested from the diet are incorporated into chylomicrons and absorbed into the lymphatic system. From here they enter the circulation, where they are bound to the DBP and lipoproteins29-30. Since endogenously synthesized vitamin D3 provide a slower hepatic delivery of the vitamin D and the more sustained increase in plasma 25- hydroxy cholecalciferol in contrast to orally administered vitamin D which associates with chylomicrons and lipoproteins and allow receptor-mediated rapid hepatic delivery of vitamin D but less sustained increase in plasma 25-hydroxycalciferol. Therefore vitamin D3 produced in the skin last 2-3 times longer in the circulation when compared with ingesting it

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