3. WHAT WILL WE KNOW?
History
Chemistry
Metabolism
Biochemical functions
Deficiency manifestations
DRA
Sources of Vitamin D
Hypervitaminosis
5. HISTORY
Reports on rickets- 2nd century AD
1650- Glisson gave a classical feature of
infantile rickets
1919- Mc Collum induced rickets in rats
by making them dietary deficient
1931- Angus & team found D3
Structure- Otto diels & Kurt Alder
6. VITAMIN D- CHEMISTRY
Group of sterols
Hormone-like
Active molecule- 1,25-
dihydroxycholecalciferol
7.
8. SYNTHESIS (SKIN)
7-dehydrocholesterol
↓UV ray (290-315 nm)
Secosterol (Ring B opens; cis
double bond between 5th & 6th C atom)
↓
Cholecalciferol (trans double
bond; rotation on 6th C atom)
9.
10. 88%- Bound to Vitamin D binding protein and
circulates
0.03%- Circulate free
Rest- circulate binding to albumin
14. Regulation of synthesis of
1,25-DHCC
1. ↓ Phosphate level-
stimulates 1-hydroxylase
activity
2. ↓ Calcium level- ↑ PTH
3. Feedback inhibition by
1,25 DHCC
4. Inhibition by 24-
hydroxylase- increased
calcitriol stimulates its
secretion and inhibits its
own synthesis
17. OTHER FUNCTIONS
Secretion of insulin
Secretion of PTH and Thyroid hormones
Inhibition of production of interleukin by
activated T-Lymphocytes
Inhibition of Ab production by B-
lymphocytes
Differentiation of monocyte precursor
cells
Modulation of cell proliferation
18. CALCIUM PHOSPHOROUS HOMEOSTATSIS
Ca :P 1:4- 4:1
Maintained by calcitriol, ALP, PTH, Calcitonin
Regulation of calcitriol- Ca, P, PTH
andcalcitriol itself
19. Synthesis and target organs are different
Different target organs
Acts through nuclear receptors like steroid
hormones
Structure and mechanism of action similar
to steroid hormones-sterol ring
Synthesis is feedback regulated
Acts in conjunction with other hormones-
calcitonin & PTH
T1/2 is short- 10 hrs; in circulation it is 2-3
weeks though.
20. Plant source- ergot-
commercial preparation
Animal source- fatty fish, fish
liver oil, egg yolk etc.
Milk is a moderate source
21.
22. D/R
Pre-school- 10 μg/ day
Children & adults- 5-10 μg/ day
Pregnancy & lactation – 10 μg/ day
> 60 yrs- 15 μg/ day
little role in osteoporosis !
25. Around 1- 1&1/2 years
Bones become soft and pliable
Craniotabes- softening of skull
bones- delayed closure of ant.
fontanelle
Frontal bossing
Bow legs, Knock knee
Rickety rosary
Pigeon chest
Kyphoscoliosis
Harrison’s sulcus
Visceroptosis
Biochemical findings- Ca & P are
low normal ; ↑↑ ALP
26. Rickets- under mineralization
Osteomalacia- demineralization
Hypophosphatemic rickets- defective P
reabsorption at renal tubules
Vit D resistant rickets- Fanconi’s
syndrome
↓ renal reabsorption of HCO3, PO4, Glucose, AA
Renal rickets- calcitriol is not
synthesised
End-organ refractoriness- abnormal or
27. Insufficient mineralization
Aged population
Rarefication of bone
Ca- slightly low; P- low; ↑↑ ALP
↑susceptibility to fractures
Vit D deficiency never causes
hypocalcemia !!!
28. With Vit A cures cold and flu
Gives good effect in COVID tt too !
Modulatory effect on immunohemopoietic
system- helps in differentiation of cells
Corrects anemia
Associated with insulin resistance & DM
Reduces risk of cancer
Reduces risk of CVD
Beneficial effects observed in AIDS
patients
31. CLINICAL CASE DISCUSSION
An 18 month old boy was brought to the
pediatrician with a complain of frequent diarrhoea
and stunted growth. The mother gave history that
the stool was somewhat sticky. The child was not
eating well and was late in walking. Mother also
gave history of frequent falls while walking and
swelling of forehead probably due to falls.
On examination: There were rachitic features.
Mother gave history of photosensitive rashes.
The pediatrician ordered for some tests. Serum
Calcium- normal, Phosphate- low, ALP- mildly
elevated
X-ray: Cupping of distal radius and distal femur,
32. More PPT on Medical Biochemistry on my
website
www.vpacharya.com