Biochem - Bone Pain Flashcards
Supply of vit D
D3 (ergocalciferol)
D2 (cholecalciferol)
Requires UVB rays
D2
Synthesised in our skin
D3
Primarily derived from our diet
Sources of vit D in our diet
Oily fish Meat Eggs Milk Fortified cereal
Distribution of plasma Ca
50% protein bound (albumin)
50% ionised
Regularatory functions of Ca
Neurotransmission Reproduction Hormone action Cellular growth Enzyme growth
Hypocalcaemia
Albumin adjusted Ca < 2.2. mol/L
Symptoms of hypocalcaemia
Paraethesia
Muscle spasm and tetany
Cardiac abnormalities
Coma
Hypercalcaemia
Albumin adjusted Ca > 2.6 mol/L
Symptoms of hypercalcaemia
Nausea Peptic ulcers Constipation Renal stones and failure Polyuria Soft tissue calcification Mental disturbance Depression
% absorption of Ca
15 - 50%
What does the percentage of intestinal Ca absorption depend on
Intake
Active absorptions
Life stage
Physiological state: growth, pregnancy, lactation
Factors affecting intestinal Ca
Vit D status and active vit D Age - postmenopausal decreases 0.21%/yr Bioavailability of food GI disorders Phosphate and phytate binding
Sources of Ca
Dairy products
Cereals and cereal products
What can Ca and vit D deficiency both cause
2’ hyperparathyroidism
Causes of Ca deficiency
Low supply - low dietary intake
Low absorption
Causes of vit D deficinecy
Low sunshine exposure Low dietary supply Low absorption Obesity High loss and/ or utilisation
Metabolism of vit D
D2, D3 –> 25OHD –> 1,25(OH)2D
Where does the hydroxylation of vit D occur
Occurs in the liver
Where does the hydroxylation of 25OHD occur
Kidney
25OHD (calcidiol)
Conc reflects balance of vit D supply and expenditure
Integrated marker of vit D supply (skin, diet, reserves)
Long half life as principally circulating form of vit D
Threshold of deficiency for plasma 25OHD
Defined as a level of plasma 25OHD above which rickets and osteomalacia are not seen
>25 mmol/L is deficient but 25-50 may be inadequate
Of a general healthy pop., groups most at risk of low 25OHD are
Dark skinned individuals Concealing dress style Little UVB exposure Obesity Adolescents Frail elderly Exclusively breast-fed babies
Spp pt groups at increased risk of low 25OHD
Renal disease GI disorders Coeliac disorders ICU pt Severe liver disease Cystic fibrosis TB
Condns caused by vit D deficiency
Rickets and osteomalacia
Muscle weakness
Cardiomyopathy
Hypocalcaemic fits
Processes affected by vit D deficiency
Chondrocyte function and apoptosis
Lack of calcification of GP cartilage
Lack of calcification of osteoid
Osteoblast, osteocyte and octeoclast function
Dx for rickets
Clinical features, radiology
Medical and diet history
Biochem - blood and urin
Bloods for rickets
25OHD
CaALB
boneALP
Urine tests for rickets
Ca
P
1,25(OH)2D (calcitriol)
Metabolically active form of vit D
Short half-life
