Metabolism

Calcium

 

Source

- ingested in diet

- absorbed in small intestine / duodenum

- under control of vitamin D

 

Excretion

- through kidney

- majority is reabsorbed

- under control of vitamin D

 

Storage

- 99% stored in bone

 

PTH

 

Source

- produced by parathyroid glands

- in response to hypocalcaemia

 

Action

 

1.  Vitamin D

- stimulates activation of Vit D in kidney

- vit D then increases absorption / decreases excretion / increases release from bone

 

2.  Bone

- stimulates release of calcium from bone by indirect inhibition osteoclasts

 

3.  Kidney

- increases resorption of calcium

- increases excretion of phosphate

 

Vitamin D

 

Generation of Vit D

 

Vitamin D3 ingested and absorbed

- activated by sunlight

- need 10 - 15 minutes 3 x per week

 

25 hydroxylated in liver

 

1 alpha-hydroxylase in kidney

- active 1,25 vit D3

- calcitriol

- this is under PTH control

 

Action Vit D

 

1.  Intestine

- increases Ca and PO4 absorption

 

2.  Kidney

- decreases Ca and PO4 excretion

 

3.  Bone

- increases Ca and PO4 release