C - Calcium metabolism Flashcards
Calcium in serum exists in 3 forms - what are they and % of each?
- Free - ionised (50%)
- Albumin bound (40%)
- Complexed (10%) to citrate/phosphate
- Normal Ca range?
- Corrected Ca2+ calculation?
2.2 - 2.6 mM/L
Serum Ca + 0.02(40-serum albumin)
Why is corrected calcium important?
If a patient has low albumin (sepsis), then calcium levels will be measured as low - even if the levels of free (active) calcium are normal.
Corrected Ca is important such that patients with hypercalcemia and a low albumin do not appear to have ‘normal’ calcium levels
PTH - it is released in response to…?
4 roles of PTH?
Released upon low free Ca+ serum
1. GUT - Ca absorption
2. KIDNEY - Ca resorption + Pi excretion
3. stimulates 1-alpha-hydroxylase
4. BONE - Ca resorption by stimulating osteoclasts
what is 1-alpha hydroxylase?
converts 25(OH)D3 into 1,25(OH)2D3 = ACTIVE CALCITRIOL
Where does vitamin D3 activation occur?
Kidney
Another tissue which can release 1-alpha-hydroxylase?
Sarcoid tissue in lung –> hypercalcemia
Roles of Calcitriol?
GUT - Ca and Pi absorption
Causes of Vit D deficiency
Renal failure (low 1-a-hydroxylase)
Anticonvulsants
No sun exposure
Poor diet
Chappatis
4 Features of Rickets
Bowed legs
Costochondral swelling
Widened epiphyses at wrist
Myopathy
4 features of osteomalacia (including biochem)
Losers zones
Increased fracture risk
Low Ca, Pi but HIGH ALP
phosphate levels in:
2ndary HyperPTH from CKD
2ndary hyperPTH from vit D deficiency
PO4 levels are:
high in CKD (inability to secrete it)
low in vit D deficiency (due to PTH being so high)
Familial benign hypercalcemia
-Level of urine Ca
- Level of plasma Ca
- Level of PTH
defect in Ca sensing receptor in parathyroid gland + kidneys
urine Ca low
plasma Ca high
PTH high
pseudohypoparathyroidism
- PTH, Ca and PO4 levels?
PTH resistance
i.e. high levels of PTH, low Ca, high Phosphate
Steps in Vit D activation with locations
Vit D –> 25 hydroxy Vit D (liver)
–> 1,25 hydroxy Vit D (kidney)
