2. VITAMIN D T
Like a hormone
Its Role in Calcium Homeostasis

3. How Does “D” Compare To Hormones?
Vitamin D3 is not secreted by a classical endocrine gland, the active form of the hormone is released from the kidney and acts at distant sites or locally.
Each of the forms of vitamin D is hydrophobic, and is transported in blood bound to carrier proteins.
Only a very small proportion of vitamin D remains in a free form in the circulation and has a serum t1/2 of about 5 hours

4. The skin
Major organ
16 % of body weight
¼ th of blood supply nourish it
Mirror of emotion
Temperature control
Infection control
Nerves protection

6. Resorption and Remodeling
Osteoclasts do this using HCL and ACID PHOSPHATASE to dissove bone matrix
Remodeling
Ostoblasts do this
Collagen fibers and hydroxyapatite matrix

7. To Make Me D, Warm Me Up and Hydroxylate Me..3X!

8. So..Exposure to Sun and Then, Fortified Foods….Give Us the D We Need

9. How Does Vitamin D Facilitate Calcium Absorption in the Intestines??

10. IN THE INTESTINE
It facilitates intestinal absorption of calcium, as well as stimulates absorption of phosphate and magnesium ions.
In the absence of vitamin D, dietary calcium is not absorbed at all efficiently.
Vitamin D stimulates the expression of a number of proteins involved in transporting calcium from the lumen of the intestine, across the epithelial cells and into blood.

11. The vitamin D form, 1,25-dihydroxcholecalciferol [1,25(OH)2D3],
1. stimulates the synthesis of the epithelial calcium channels in the plasma membrane calcium pumps , and
2. induces the formation of the calbindins.

12. Vitamin D: Its Role is ABSORPTION of CALCIUM ,and to a lesser extent, Phosphorous, from the Small Intestine and Duodenum.

13. Once joined with ingested vitamin D, facilitate increased serum calcium levels .
Shows Expressed Calbindins and How the facilitate transport of Calcium through the Membranes

14. Calcium Absorption Enhanced by Carrier Protein Calbindin

15. Calcium absorption is transport across the epithelial cell, which is greatly enhanced by the carrier protein calbindin, the synthesis of which is totally dependent on vitamin D

16. Calcitriol Raises Blood Calcium in 3 Ways:
Increases Ca++ absorption by the small intestine.
Increases Calcium (and Phosphate ) resorption from the skeleton. It binds to hematopoietic stem cells and causes differentiation of osteoclasts.
3. Weakly promotes the reabsorption of Calcium ions by the kidney cells (less calcium excreted)

17. Let’s Look A Bit Closer at RANK L

18. But, I thought Vitamin D HELPED US retain Calcium?
Yes, It does. So, although there is some proliferation of osteoclasts the
NET RESULT IS:
CALCIUM ABSORPTION and REMODELING….Outweighs RESORPTION…. Because…

19. Vitamin D

20. Vitamin D is not strictly a vitamin.
It can be synthesized in the skin.
Under most conditions that is the major source of the vitamin.
Dietary source required, only when
sunlight exposure is inadequate .

21. Major Role
Its main function is in the regulation of calcium absorption and homeostasis.
Most of its actions are mediated by way of nuclear receptors that regulate gene expres­sion.

22. Role in regulating cell proliferation and differentiation
There is some scientific evidence available now that intakes considerably higher than RDA maintain better calcium homeostasis, reduce the risk of insulin resistance, development of obesity and various cancers.

23. Vitamin D Is Synthesized in the Skin
7-Dehydrocholesterol (intermediate in the synthesis of cholesterol that accumulates in the skin) undergoes a nonenzymic reaction on exposure to ultraviolet light, yielding previtamin D.

25. Factors affecting Vit. D synthesis
The amount of Vit D formed by the action of sunlight on the skin is dependent on
Intensity of light
Length of exposure
Skin pigmentation

26. ABSORPTION
This undergoes a further reaction over a period of hours to form cholecalciferol, which is absorbed into the bloodstream.
In temperate climates, the plasma concentration of vitamin D is highest at the end of summer and lowest at the end of winter.

28. Metabolism
Vitamin D Is Metabolized to the Active Metabolite, Calcitriol, in Liver & Kidney.
Cholecalciferol, either synthesized in the skin or from food, undergoes two hydroxylations to yield the active metabolite, 1,25-dihydroxy vitamin D or calcitriol.
This is released into the circulation bound to a vitamin D binding globulin, which is the main storage form of the vitamin.

30. Alternate product
In the kidney, calcidiol undergoes either 1- hydroxylation to yield the active metabolite 1,25-dihydroxy-vitamin D (calcitriol), or 24-hydroxylation to yield a probably inactive metabolite, 24,25-dihydroxyvitamin D (24-hydroxycalcidiol).

31. Functions
Vit D plays a major role in the regulation of calcium and phosphate metabolism by promoting their intestinal absorption, influencing the process of bone mineralization.

32. Functions
Vitamin D exerts its anti ricket action by making the intestinal mucosa permeable to calcium and phosphorus and facilitating the active transport of calcium across cell membranes.

33. Vitamin D occurs in two forms
“Vitamin D2” (ergocalciferol),
chief Vit D precursor in plants is, ergostreol.
2 “Vitamin D3” (cholecalciferol),
the main form occurring in animal cells and developing in skin on exposure to ultraviolet light from 7- dehydro cholesterol

34. Animal sources of Vit D
Eggs
Fish Liver oil
Butter
Fish

35. Stability
Vit D is stable through storage, processing and cooking and is absorbed effectively from GIT
Any abnormality in fat absorption may cause mal- absorption of Vit D

36. Metabolism
Before it can function, Vit D3 must be activated by hydroxylation which takes place both in liver & kidney.
The initial conversion in the liver results in 25-hydroxy cholecalciferol (cacidiol), the major circulating form of Vit D3.

37. Metabolism
2nd hydroxylation takes place in the proximal tubule of the kidney, giving rise to 1,25-dihydroxycholecalciferol or calcitriol.
This form is then transported to bones, kidneys and intestines.

38. Recommended Daily Allowance
400 iu (10ug) of Vit D per day promote optimal calcium absorption and enhance growth
Higher level is recommended for infants and children

39. Recommended Dietary Allowances
Infants 0 – g
0.5 – g
Children 1 – g
4 – g
7 – g

40. Recommended Dietary Allowances
Adults Male Female
11 –
15 –
19 –
23 –
Pregnancy
Lactation

41. Effects of deficiency
A deficiency of Vit D causes impaired intestinal absorption of calcium and phosphorus and faulty mineralization of teeth and bones.
2. Skeletal malformation result from the inability of the softened bone to withstand weight bearing . In children this bone condition is termed rickets.

42. Effects of deficiency
In adults this bone condition is termed as osteomalacia and is caused purely by lack of Vit D and calcium.
Particularly prevalent among pregnant and lactating oriental women.

43. Effects of deficiency Other symptoms of rickets include
Delayed closure of the fontanelles (suture lines in the skull) especially in premature infants
Projection of sternum (pigeon breast).
Spinal curvature and
Bowing of the legs

44. Effects of deficiency
Vit D is involved in neuro-muscular activity and its deficiency causes tetany characterized by convulsions, muscle twitching and sharp flexion of the wrest and ankle joint.

45. Effects of deficiency
4.This condition may also result from parathyroid disease or from insufficient dietary intake or intestinal absorption of calcium or Vit D
5. Dental caries are more prevalent among children with poor intakes of Vit D, calcium and phosphorus.

46. Toxic Effects Precisely not known It is potentially lethal vitamin.
Toxicity symptoms include
Polyurea
Nocturia
Weight loss
Diarrhea &
Nausea

47. Severe toxicity results in
Calcification of soft tissues such as
Blood vessels
Heart
Stomach
Bronchi &
Kidney