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