Vitamin D Lecture 2 BIOCHEMISTRY

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Vitamin D Lecture 2 BIOCHEMISTRY

  1. 1. Dr. Vijay Marakala, MBBS, MD. Assistant professor BIOCHEMISTRY SIMS & RC Sunshine vitamin
  2. 2. Chemistry Sources RDA Metabolism Functions Deficiency Toxicity
  3. 3. PROVITAMIN 7- Dehydrocholesterol Ergosterol VITAMIN Vitamin D3 [Cholecalciferol] Vitamin D2 [Ergocalciferol] Vitamin D is a sterol
  4. 4. 200 – 400 IU /day [5 – 10µg/day] 1microgram of vitamin D = 40 International Units
  5. 5. Forms D3 D2 Site Upper small intestine Mechanism Along with lipids Requires bile salts ABSORPTION
  6. 6. TRANSPORT Binding to vitamin D binding globulin
  7. 7. Synthesis of active form of vitamin D 1, 25-dihdroxy cholecalciferol or calcitriolACTIVE FORM
  8. 8. 1- α- hydroxylase
  9. 9. Calcitriol is the biologically active form of vitamin D Regulation of plasma calcium and phosphorus
  10. 10. Action of calcitriol on the intestine Action of calcitriol on the bone Action of calcitriol on the kidney
  11. 11. Action of calcitriol on the intestine • Increases the intestinal absorption of calcium and phosphate • By increased synthesis of calcium binding protein
  12. 12. Action of calcitriol on the bone • Mineralization of bone at low doses • Mobilization of calcium from bone at high doses
  13. 13. Action of calcitriol on the kidney • Increased reabsorption of calcium and phosphorus • Decreased excretion of calcium and phosphorus
  14. 14. Causes Inadequate supply Impaired absorption Impaired production of 25hydroxy vitamin D3 Impaired production of 1, 25 dihydroxy vitamin D3 Resistant to the effects of 1, 25 dihydroxy vitamin D3
  15. 15. CLINICAL FEATURES Children Adults Children Rickets Adults Osteomalacia
  16. 16. Features Delayed milestones Delayed closure of anterior fontanelle Delayed dentition Deformities of bones Decreased serum calcium
  17. 17. Bone deformities Craniotabes Frontal bossing Rachitic rosary Pegion chest Knocked knee Bowed legs
  18. 18. Frontal bossing
  19. 19. Fig. 7-5a, p. 222 Bowed legs – Characteristic of rickets
  20. 20. Fig. 7-5b, p. 222 Beaded ribs – Characteristic of rickets
  21. 21. Rachitic rosary
  22. 22. Causes Inadequate exposure to sunlight Inadequate dietary intake Features Demineralization occurs mainly in spine, pelvis and lower extremities Increased softness & susceptibility to fracture Bowing of long bones
  23. 23. Causes Over ingestion Features Hyper calcemia Metastatic calcification

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