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And I welcome you in responding to me Marie Anne. Hi !

The following would be of some explanation:
Dinosaursgo AWOL... Astronauts in the NFZ ( No Fly Zone ).

" A hormone is a chemical messenger thatis produced and secreted by specific glands and cells within the body ofanimals. After secretion of the hormone, it is transported through thebloodstream to designated target organs where the hormone by binding toits specific receptor delivers its "message" to that set of cells. Thesecells then promptly produce biological responses specific for that hormone."

I agree with your response but it is saying"A hormone is a chemical messenger that is produced and secreted by specificglands and cells within the body of animals. "

These are the words that I don't like in thedefinition when they pertain to Vitamin D, 'chemicalmessenger', 'produced','secreted', 'specific glands'and 'cells' .

As I understand it, CHOLESTEROL is under yourskin. An enzyme transforms it to
7-DEHYDROCHOLESTEROL.( Link on the left will take you to a previous post. The 7-DEHYDROCHOLESTEROLimage there will link you to ExPASy Biochemical Pathways. The same imagewill appear. Use the direction arrows to navigate like a city map. )

A narrow window of energy allows a photochemicaltransformation ( absorption of ULTRA VIOLET light at certain frequencies) to take place. Absorption of energy into
the double bonds of the second cyclic ringbreaks the opposite side open. Rotation at the single carbon bond betweenthe two double bonds occur and a new substance forms,
VITAMIND3
If over irradiation occurs in chemical synthesis( commercial process ) you get
TOXISTEROLand SUPRASTEROLS I and II . The series is the same for the over
irradiation of 7-DEHYDROCHOLESTEROL. Novelways of irradiation of 7-DEHYDRO
sterols to VITAMINS D were researched, differentarc sources, high-frequency electrical
discharge,....nuclear irradiation. The lastproduced some unusual forms of VITAMINS D
but were never thoroughly researched and testedin bioassays. They were very potent.
In this instance, it would be the radiolyticchemistry of sterols and of the
( VITAMINS D ).

A binding protein picks up VITAMIN D3andit is then tranported to the liver. Another enzymeinitiates hydroxylation to occur at the 25th CARBON of the side chain ofVITAMIN D3 .We get our first intermediate metabolite 25-HYDROXYCHOLECALCIFEROL.As reference with MERCK( VITAMIN D )
" It passes through the enterohepatic circulation and is reabsorbedfrom the gut. "
which means that the liver is doing its duty in getting rid of it.Because it is hydrophobic and fat soluble the next stage begins. MERCK( LIVER-GALLBLADDER )
25-HYDROXYCHOLECALCIFEROL is reabsorbed withbinding protein and ends up in the kidneys. Here an enzyme assistsin hydroxylation at the 1st CARBON and it becomes the active hormone form,1alpha,25-DIHYDROXYCHOLECALCIFEROL or
CALCITRIOL.

It is interesting to note that the syntheticanalog is
1 alpha-HYDROXYCHOLECALCIFEROL there is nohydroxyl group at the 25th CARBON. This form is " the hormonal formof VITAMIN D3, which shows identical
potency with respect to stimulation of intestinalcalcium absorption and bone mineral
mobilization. " The natural form is 1alpha,25-DIHYDROXYCHOLECALCIFEROL.
The human or animal wants to get rid of atoxic substance after primary hydroxylation and does so, but then it getsreabsorbed. Maybe some gets excreted but the small amont that gets to thekidneys for secondary hydroxylation becomes a very potent product.

I am trying to understand that the active formis produced when the kidneys assist in
hydroxylation of the 1st CARBON. At this pointit is called a
STEROID HORMONE.

Are the terms of the definition being fufilled.A chemical transformation as that of hydroxylation is creating a SteroidHormone ? EndocrineGlands ? You will have to read this through.

Sex Steroid Hormones follow in pathways afterCHOLESTEROL formation.
PROVITAMIN D ( 7-DEHYDROCHOLESTEROL) by theory occurs before
CHOLESTEROL formation. Sterols are liquidcrystals and the majority have the same
nuclear structure.

Now let us look at VITAMIN D
Would you agree that the simple old 1,3-BUTADIENEis :

H2C==CH---CH==CH2

The complex and exotic 1,3-BUTADIENES as VITAMINSD.
1. Goto
2. Goto
3. Goto
A divinyl bridge ( 1,3-BUTADIENE ) with the 1 and 3 CARBONS substitutedwith the
lower and the upper portion of CHOLESTEROL

http://www.nutritionfarm.com/focus/structure%20images/vit_D3.gif-------->