Vitamin D Vitamin D

CHOLESTEROL CHOLECALCIFEROL

A

C D

B

SYNTHESISSYNTHESIS

REGULATION OF SECRETION REGULATION OF SECRETION OF vit DOF vit D

-ve Feedback -ve Feedback MechanismMechanism

Other sites of Other sites of Calcitriol synthesisCalcitriol synthesis

Placenta Keratinocytes Macrophages

Mechanism of ActionMechanism of Action

ACTIONS OF VIT DACTIONS OF VIT DIntestinal Ca absorptionIntestinal phosphate absorptionRenal excretion of Ca and

phosphateAction on bone

Applied AspectApplied AspectRickets and OsteomalaciaVit D resistance ricketsOsteoporosis

PTHPTH

ANATOMYANATOMY

SYNTHESISSYNTHESIS

SECRETION

Other factors – calcitriol , phosphate, Mg

MECHANISM OF ACTION MECHANISM OF ACTION

ACTIONSACTIONSEffect on calcium and phosphate

concentration in ECFAbsorption of calcium and

phosphate from boneExcretion of calcium and

phosphate by kidneyIntestinal absorption of calcium

and phosphateAction on other ions

Applied Applied HypoparathyroidismHyperparathyroidismPseudohypoparathyroidism

Hypoparathyroidism Hypoparathyroidism Cause – ThyroidectomyChvostek′ sign Trousseou′s sign

HYPERPARATHYROIDISHYPERPARATHYROIDISMM Parathyroid poisoning

PTHrPPTHrPSite of synthesis – uterus , enamel ,

brain , Keratinocytes , smooth muscle

Action1.Growth and development of

cartilage in utero2.Transport of Ca in placenta3.Skeletal development4.Inhibit excitatory damage to

developing neuron

CALCITONINCALCITONIN

SECRETIONSECRETION

Stimulators1.Plasma Ca2.β- adrenergic agonist3.Dopamine4.Estrogen5.Gastrin6.CCK – PZ7.Glucagon8.Secretin

ACTIONACTIONBoneKidneyGITPhysiological significance

Calcium HomeostasisCalcium Homeostasis

↓ Plasma Ca

↑ PTH secretion from parathyroid gland

↑Plasma PTH

KIDNEY↑Ca reabsorption ↑1,25 DHCC

Bone↑Resorption

↓Urinary excretion of

Ca↑plasma 1, 25 DHCC

↑Release of Ca into plasma

↑Ca absorption in intestine

Restoration of plasma Ca towards normal