1. Vitamin D
Dr.S.Chakravarty ,MD

2. Vitamin D
(yeast) Vitamin D2 : Ergosterol (pro D2)  Ergocalciferol (D2) added to milk and dairy.
(Human) Vitamin D3 : Pro (7-dehydrocholesterol)  Pre (9,10-secosterol)  (D3) cholecalciferol.
7-Dehydrocholesterol is present in epidermis and dermis.
Short exposure of UV light nm converts pro to pre vitD3  enters blood circulation and equilibrates to D3.

3. Sunlight
Prolonged exposure to sunlight leads to conversion of previtamin D3 to Lumisterol and Tachysterol.
Seasonal variation – more UV at the end of winter in cold countries.
Geographical variations
Other Considerations :-
Sunscreens :-In labs tests with Sunscreen lotions block UV and decrease production of vitamin D3.
But because people who use more sunscreen spend more time in the sun, so naturally they will have higher vitamin D levels.

4. Activation of vitamin D3 :
skin

5. X CIRRHOSIS , LIVER FAILURE
7-Dehydrocholesterol
Dietary source required if insufficient exposure to UV light.
SKIN :-UV Light
CHOLECALCIFEROL
X CIRRHOSIS , LIVER FAILURE
LIVER :- 25 hydroxylase
HYPOCALCEMIA
25 hydroxycholecalciferol
(+)
X CRF, END STAGE RENAL DIASEASEc
+PARATHYROID
KIDNEY :- 1 α hydroxylase(induce )
1,25 dihydroxy cholecalciferol
Vit D
Kidney :-
Vit D : Retention of Ca+2
PTH :- Conserves Ca+2 at expense of PO4-3
Bone :- Osteoclasts ; Ca+2
Mineralization(with PTH)
Duodenum: Increase calcium uptake from intestine

6. Calcium metabolism:
Calcium is stored as calcium-hydroxy-appetite crystals in bone.
99% present in bone – which maintains serum calcium levels of ( mg/dl)
5 mg is ionized calcium – physiologically important
mg is bound to serum albumin (0.8mg /gm of albumin)
1mg exists as bound to anions (citrate).

7. Functions of calcium: Intracellular Extracellular Second messenger
Muscle contraction
Membrane excitability
Degranulation and release of hormones.
Co-factor in enzyme activity.
Nerve impulse transmission
Coagulation cascade
Maintains intracellular conc.
Deposition of calcium in bone from diet.

8. Role of vitamin D in calcium homeostasis:
Vitamin D binds selectively to retinoic acid X receptor (RXR) by a Zinc finger motif -- mRNA production  synthesis of
Epithelial calcium receptor
Calbindin in intestines leading increased calcium absorption.
Role of PTH:
Stimulate Osteoblast to produce RANK-L and alkaline phosphatase  binds to RANK receptor on monocyte to form osteoclasts  HCl secretion and demineralization of bone.
Receptor Activator of Nuclear Factor κ B

9. What happens in Hypocalcemia :
Increase in PTH secretion and decrease calcitonin.
Increased distal tubular re-absorption of calcium and excretion of phosphate:
Increase 1α-hydroxylase activity of kidney.
Increase 1,25 dihydroxy cholecalciferol  increased absorption in the small intestine.
Increased Osteoclastic activity bone resorption and increased calcium in circulation.

10. During Hypercalcemia :
Release of calcitonin  inhibits the activity of osteoclasts
Decrease in PTH and Decreased 1,25 -Dihydroxycholecalciferol  decreased renal and intestinal absorption.
Bone formation due to supersaturation of calcium and phosphate.

11. Vitamin D deficiency:
Hypocalcemia and hypophosphatemia : poor mineralization and stunted growth
Rickets : children
Widening of growth plate – rachitic rosary at the costchondral junction.
Craniotabes – ping pong skull
Bow legs or knocked knees – bending of long bones due to poor mineralization.
Reduced radio-opacities on long bones.
Lax muscles – protruberant abdomen.

12. Osteomalacia Seen in adults
Looser’s zone or pseudofractures seen in scapula, pelvis and femoral neck.
Soft, flexible, brittle, deformed bones
Progressive weakness
Pain in pelvis, lower back, and legs

13. Other functions of VIT D:
Regulation of cell growth – Cancer prevention
Regulation of immune function – prevents autoimmune disease
Regulation of blood pressure – prevents heart disease

14. Hypervitaminosis D: Similar to features of hypercalcemia:
Constipation, polyuria, polydipsia, confusion
Calcinosis of soft tissues – metastatic calcification.
Renal stones

15. Thank you