This document discusses vitamin D, calcium, parathyroid hormone, and calcitonin. It covers their roles in calcium regulation and bone health. Vitamin D is a fat-soluble vitamin that is synthesized in the skin from cholesterol or ingested from plants and animals. It is metabolized in the liver and kidneys to its active form calcitriol, which increases calcium absorption from the intestine and bone resorption. Parathyroid hormone increases serum calcium levels by promoting bone resorption and renal calcium reabsorption. Calcitonin has the opposite effect of parathyroid hormone by inhibiting bone resorption and promoting calcium deposition in bone. Together these elements work to maintain adequate calcium levels in the blood

1. VITAMIN D
DR SHARAN

2. INTRODUCTION
Fat soluble vitamin
Sterol
Function like hormone
• Forms
Ergocalciferol – vitamin d2
Cholecalciferol – vitamin d3

3. • Distribution
Ergocalciferol – plants
Cholecalciferol – animals
Referred as pro vitamin
They differ from each other only in presence of
additional double bond and methyl group

5. Cholesterol biosynthesis 7 dehydrocholesterol
Sun
Cholecalciferol

6. ABSORPTION
• Absorbed in small intestine
Vit d2 and d3 mixed with micelles by combining
with bile salts
Mixed micelles are presented to mucosal cells
Absorption by passive transport

7. TRANSPORT

8. METABOLISM
• Cholecalciferol hydroxylated at 25th position to 25
hydroxy cholecalciferol in liver
• 25 hydroxy cholecalciferol at position 1 to form
1,25 dihydroxy cholecalciferol and at 24 position
to form 24,25 dihydroxy cholecalciferol
• It has 3 carbons 1,3 and 25 hence called calcitriol

10. REGULATION
• 1,25 dihydroxy cholecalciferol is regulated by 1
alpha hydroxylase
• Its activity is increased in hypocalcemia
Which inturn stimulates pth secretion leading to
increase 1 alpha hydroxylase

12. RDA
• Children - 10 mg/day or 400 iu
• Adults – 5 mg /day or 200
- 10 mg/day or 400
• >60 yrs – 600 iu

14. FUNCTION
MAINTAIN ADEQUATE LEVEL OF CALCIUM IN
PLASMA
• INCREASE UPTAKE OF CALCIUM BY ABSORPTION
FROM INTESTINE
• VIT D ALONG WITH PARATHYROID HARMONE
HELPS IN BONE FORMATION WHICH CAUSES
ELEVATION OF CALCIUM
• MINIMIZE THE EXCRETION PF CALCIUM AND
PHOSPHATES AND ENHANCING REABSORPTION

15. CLINICAL IMPORTANCE
• Nutritional rickets
Demineralization of bone
Decreased serum calcium (9 – 11 mg / dl)
Decreased plasma phosphorous (3 to 4.5 mg /dl)

17. • Renal rickets
Chronic renal failure
Inability to synthesis 1 alpha hydroxylase
• High consumption
Calcinosis
Loss of appetite
Nausea
Lathergy
Loss of weight

18. CALCIUM

19. INTRODUCTION
• Most abundant
1 – 1.5 kg
99%
Bone and teeth
1%
Skeletal tissue

21. BIOCHEMICAL FUNCTION
• Development
• Muscle contraction
• Blood coagulation
• Nerve transmission
• Membrane integrity and permeability
• Activation of enzyme
• Release of hormone
• Secretory process
• Contact inhibition
• Action on heart

22. DIETARY REQUIREMENT
• ADULT – 800 mg
1.5 gm
• CHILDREN - .8 TO 1.2 g
• INFANTS – 300 TO 500 mg

23. • Calcitriol
• PTH
• Calcitonin

24. SOURCE
• BEST
MILK AND milk products
• GOOD
BEANS
VEGETABLES
FISH
EGG YOLK
CABBAGE

27. PARATHYROID HARMONE

28. PARATHYROID HARMONE
• Secreted by 2 pairs of parathyroid glands
Single chain polypeptide
84 amino acids
PREPRO PTH 115
PRO PTH 90
ACTIVE PTH 84

29. MECHANISM
• PRIME FUNCTION
ELEVATE SERUM CALCIUM
• 3 INDEPENDENT TISSUE
Bone
Kidneys
Intestine

30. • Bone
Demineralization of bone by osteoclasts
Increased activity of Enzymes pyrophosphates and
collagenase
• Kidneys
Increases ca resorption
Promoting production of calcitriol
• Intestines
Synthesis of calcitriol

31. • Excess activity of the parathyroid gland causes
rapid absorption of calcium salts from the bones,
with resultant hypercalcemia in the extracellular
fluid
• conversely, hypofunction of the parathyroid glands
causes hypocalcemia, often with resultant tetany.

32. MECHANISM

34. CALCITONIN

35. CALCITONIN
• Peptide
32 AA
Antagonist of PTH mechanism
Promotes calcification ( osteoblast )
Decreases bone resorption and increases calcium
excretion

37. CLINICAL IMPORTANCE
• Hypercalcemia
• Hypocalcemia
• Rickets
• Renal rickets
• Osteoporosis
• Osteopetrosis
• Paget’s disease ,
in which osteoclastic activity is greatly accelerated,
calcitonin has a much more potent effect of
reducing the calcium absorption.