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
