Calcium Haemostasis

Haemostasis
Skeleton = 1kg/25000mmol/99% body Ca
Dietary Intake of Ca = 25mmol/day
Exchange between ECF and bone = 10mmol/day
*renal (imp in regulation)
GIT... also involved

Pathology
... occus with...
- Gut, renal, skeletal problems
- Parathyroid disorders
- Abnormal Vitamin D metabolism

Ix
*Total plasma calcium
plCa = alb-bound 40%, complexed 10%, free ionised fractions 50%
Ionised Ca = active fraction - roles in bone, teeth, neuromuscular activity, coagulation (enzyme co-factor)

Corrected Ca = Ca + 0.02(40-Albumin)


Parathyroid Hormone
Increase in PTH - stim by
 - low Ca
 - raised PO4 (Chronic effect only)
Only intact PTH is active
...act on...
Kidneys
 - incrs Ca reabsorption
 - decrs PO4 reabsorption
 - decrs HCO3 reabsorption
 - incrs 1-alpha-hydroxylation of vit D (activated)
Bone
 - incrs osteolclastic resorption


Vit D
Dermal synthesis & Diet
Liver = 25-OH cholecalciferol - 'inactive'
Renal = 1,25 dihydroxycholecalciferol (calcitriol - 'active')
Calcitriol stim by...
- low ionised Ca (via PTH)
- low PO4
- low vit D
Calcitriol acts on...
- gut = incrs Ca & PO4 absorption
- renal = incrs Ca & PO4 reabsorption
- bone - incrs resorption/mineralisation, remodelling


Calcitonin (Thyroid 'C' Cells)
hCa actions
- stim by increased Ca ions