vitamin d lecture 2 biochemistry
TRANSCRIPT
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VITAMIN D[CHOLECALCIFEROL]
Dr. Vijay Marakala, MBBS, MD.
Assistant professor BIOCHEMISTRY SIMS & RC
Sunshine vitamin
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VITAMIN D
Chemistry Sources RDA Metabolism
Functions Deficiency Toxicity
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VITAMIN D - CHEMISTRY
PROVITAMIN
7- Dehydrocholesterol
Ergosterol
VITAMINVitamin D3
[Cholecalciferol]
Vitamin D2
[Ergocalciferol]
Vitamin D is a sterol
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VITAMIN D - SOURCES
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VITAMIN D - RDA
200 – 400 IU /day[5 – 10µg/day]
1microgram of vitamin D = 40 International Units
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VITAMIN D - METABOLISM
Forms
D3
D2
Site
Upper small intestine
Mechanism Along with
lipids
Requires bile salts
ABSORPTION
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VITAMIN D - METABOLISM
TRANSPORT
Binding to vitamin D binding globulin
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VITAMIN D - METABOLISM
Synthesis of active form of vitamin D
1, 25-dihdroxy cholecalciferol or calcitriolACTIVE FORM
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1- α- hydroxylase
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VITAMIN D - FUNCTIONSCalcitriol is the biologically active form of
vitamin D
Regulation of plasma calcium and phosphorus
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VITAMIN D - FUNCTIONS
Action of calcitriol on the intestine
Action of calcitriol on
the bone
Action of calcitriol on the kidney
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VITAMIN D - FUNCTIONS
Action of calcitriol on the intestine• Increases the intestinal absorption
of calcium and phosphate• By increased synthesis of calcium
binding protein
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VITAMIN D - FUNCTIONS
Action of calcitriol on the bone• Mineralization of bone at low doses• Mobilization of calcium from bone at high doses
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VITAMIN D - FUNCTIONS
Action of calcitriol on the kidney• Increased reabsorption of
calcium and phosphorus• Decreased excretion of calcium
and phosphorus
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VITAMIN D - DEFICIENCY
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
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VITAMIN D - DEFICIENCY
CLINICAL FEATURES
Children
Adults
Children
Rickets Adults
Osteomalacia
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RICKETS
Features Delayed milestones
Delayed closure of anterior fontanelle
Delayed dentition
Deformities of bones
Decreased serum calcium
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VITAMIN D - DEFICIENCYBone deformities
Craniotabes
Frontal bossing
Rachitic rosary
Pegion chest
Knocked knee
Bowed legs
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Frontal bossing
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Fig. 7-5a, p. 222
Bowed legs – Characteristic of rickets
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Fig. 7-5b, p. 222
Beaded ribs – Characteristic of rickets
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Rachitic rosary
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OSTEOMALACIA
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
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OSTEOMALACIA
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VITAMIN D TOXICITY
Causes
Over ingestion
Features
Hyper calcemia Metastatic calcification
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