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