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peaking of the way sunlight works at
the skin level, one has to recall that as a traveling energy, light effect on
skin depends on the wavelength like anywhere else. Sunlight keeps giving the
skin a youthful glow, even though UV radiation is harmful with bad
consequences. So said, light happily affects the skin through physiological and
vital processes. The more interesting of the process remains vitamin
D synthesis.
Besides being a protective shield
and a visible ID oriented to social life, human skin is
the site of the sunlight-generated vitamin D. Vitamin D remains a crossroad of
our health system, aiming at maintaining homeostasis balance. This sunlight
–bounded synthesis emphasizes the way human life among other
things is related to sky-located energy.
A lot has to come again
about light regarding the role of this vitamin
in biology, a vital one, to tell the truth. Vitamin D synthesis
starts at skin level when UVB hits the epidermal cells causing a change to a
cholesterol molecule. Then, crossing the circulation, this new synthesized
molecule goes to the liver before being transformed into the 25-hydroxyvitmin
D. Let’s recall that there exists to types of vitamin D, the 25-OH D3 named the
storage form and the 1-25(OH)2 D3, the active form. This last one has been
elaborated through the kidney and is considered physiologically active,
implying this way its hormonal function. It is called calcitrol.
This hormone intervenes in the regulation of Ca+ 2 and Po4 . Both of them are
absorbed into the gut.
Given the overall function of
calcitrol in human physiology via the parathyroids and the bones, it is
regarded as a key hormone affecting the cardiac cycle as well as the basal
metabolism through the thyroid function and calcium and phosphate
regulation. From this point of view we can ask what
would have happened to life if sunlight had failed to
trigger the vitamin D synthesis. As put by the PhD Laurance
Johnson,” the sunlight –generated hormone sustains health throughout the body”.
FOOTNOTES
VITAMINE D Photochemistry
Photochemical conversion of
7-dehydrocholesterol to previtamin D3
Thermal isomerization of previtamin D3 to vitamin D3
1 ) The transformation that converts 7-dehydrocholesterol to
Vitamin D3 (cholecalciferol) occurs in two steps.
First, 7-dehydrocholesterol, is photolyzed by ultraviolet light in a
6-electron conrotatory electrocyclic
reaction. The product isprevitamin D3.
Second, previtamin D3 spontaneously isomerizes to vitamin D3 (cholecalciferol) in an antarafacial sigmatropic [1,7]
hydride shift. At room temperature, the transformation of
previtamin D3 to vitamin D3 takes about 12 days to complete.
2 ) Vitamin D can be synthesized only via a
photochemical process, so land vertebrates had to ingest foods that contained
vitamin D or had to be exposed to sunlight to photosynthesize vitamin D in
their skin to satisfy their body's vitamin D requirement
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