vit D

1. CHEMISTRY, SOURCES,
SYNTHESIS & FUNCTION
OF VITAMIN D
NUR FARRA NAJWA BT ABDUL AZIM
082015100035

2. OBJECTIVES
 By the end of the seminar student should be
able to understand the
 CHEMISTRY (STRUCTURE)
 SOURCES
 SYNTHESIS
 ACTIVE FORM
 ACTIONS (FUNCTIONS)

3. INTRODUCTION
 Vitamin classified
 Fat soluble vitamins (VIT A, D, E, K)
 Water soluble vitamins (VIT B Complex, VIT C)

4. CHEMISTRY OF VIT D
 Derived from 7-dehydro-cholesterol or ergosterol
via action of sunlight
7-dehydrocholesterol is intermediate in minor
pathway of cholesterol synthesis (Malphigian layer
of epidermis)
 In skin, the ultraviolet light break the bond in
7-dehydrocholesterol
 Form provitamin (secosterol)
 Provitamin isomerised
 Form vitamin D3 (cholecalciferol)
“SUN-SHINE VITAMINS”

7. SOURCES OF VIT D
 Skin
 Directly exposure to
sunlight
 Commercially derived
from fungus, ergot
-skin largest
organ
-16% body weight
-vitamin d
deficiency seen in
winter
In winter,
wavelength of UV
rays shifted to
longer wavelength
due to increase in
solar zenith angle

8. SYNTHESIS OF VIT D
Calcitriol
- 3 OH group
at 1, 3, 25
position

9. SYNTHESIS OF VIT D
 Prohormone (vit d) transported to LIVER
 Hydroxylated at 25th position
 Form 25-hydroxy cholecalciferol (major storage
form)
 Hepatic 25-hydroxylase (microsomal oxygenase)
 In plasma, bind to VDBP (Vit D binding protein)
 In kidney, further hydroxylated at 1st position via
1-α hydroxylase
 Form 1,25-dehydrocholecalciferol
CALCITRIOL

10. (IN SKIN)

11. ACTIVE FORM
 Calcitriol

12. ACTIONS OF VIT D
 Sites of actions
 Intestinal villi cell
 Bone osteoblast
 Kidney distal tubular cells

13. A) Intestinal Villi Cells
Promotes
calcium
absorbtion
from gut
lumen
From
brush
border,
absorbed
passively
From
Intestinal
cell
absorbtion
needs
energy
Absorbtion to
blood via
sodium-
calcium
exchanger or
via pumping
out the calcium
calbindin
complex
Calcitriol
act like
steroid
hormone
Enters
target cell
and bind
to
cytoplasmi
c
receptors
HR
complex
interact
with DNA
More
calbindin
leads to
more
calcium be
absorbed

15. B) Bone Osteoblast
 Increase osteoblastic activity (mineralization) and
bone deposition
 Regulates remodelling action of osteoblast and
osteoclast
 Produce
 Osteoclast differentiation from multinucleated cell of
osteoblast lineage
 Stimulates osteoblast alkaline secretion
(phosphatase)
 Lead the increase of
 concentration of phosphate
 ionic product of calcium phosphate

17. C) KIDNEY DISTAL TUBULAR
CELLS
 Increase tubular reabsorbtions of calcium and
phosphorus
 Hence, mineral conserved

18. SUMMARY