Calcium Disorders Flashcards
Calcium function
Bone mineralization
Blood clotting
Muscle contraction
Nerve function + neurotransmission
Serum calcium levels
2.2-2.6 mmol/L
Calcium state
Most serum calcium bound to plasma proteins (mainly albumin)
Only unbound calcium is biologically active
Serum calcium always needs to be corrected for albumin concentration
Serum calcium + albumin conc
+/- 0.02 mmol/L for every gram that albumin is below/above 40g/dL
Calcium hormonal regulation
Vitamin D
Parathyroid hormone
(calcitonin)
Vitamin D conversion
Vitamin D3 (cholecalciferol) - synthesizes in sun-exposed epidermis
Requires 2 activation (hydroxylation) steps
Liver- 25 hydroxycholecalciferol (majority Vit D in this form)
Kidney- 1,25-dihydroxycholecalciferol (calcitriol)
Majority of Vit D is in this form
25-hydroxycholecalciferol
Vit D bound
25-dihydroxycholecalciferol mostly bound to plasma proteins
1,25-dihydroxycholecalciferol largely unbound
1,25-dihydroxycholecalciferol half life
Short
15 hours
Calcitriol binds to
Nuclear vitamin D receptors
Vit D in Gut
Vit D increases the absorption of dietary calcium and phosphate
Vit D in kidney
Increases calcium and phosphate reabsorption
Vit D in bone
Stimulates osteoclasts to release calcium and phosphate
Parathyroid gland
4 parathyroid glands
PTH
Secreted by chief cells within parathyroid gland
Released in response to low calcium levels
Can also be stimulated by changes in phosphate concentration
Acts to increase serum Ca
PTH on Kidney
Increases Vit D
Increases Ca and Hydrogen reabsorption
Decreases phosphate and bicarbonate reabsorption