Chem path 1 - calcium metabolism Flashcards
What % of calcium is in the serum?
1%, the other 99% in the bone
What are the 3 forms in which calcium can be found?
Free, ionised (50%) (biologically active, maintained at a fixed level) Albumin bound (40%) Complexed with citrate/phosphate (10%)
What is the equation for corrected calcium?
Corrected calcium = Serum Ca + 0.02 (40-albumin g/l)
What can corrected calcium be used for?
To show if the problem with calcium is to do with albumin or not
What will happen to calcium if albumin is low?
Bound calcium will be low but free calcium will be normal
What are the actions of PTH?
1 alpha hydroxylation of vit D –> calcidiol to calcitriol –> increased gut absorption of calcium AND phosphate
Bone: osteoclast activation
Direct renal calcium resorption and phosphate excretion
Two main hormones involved in calcium homeostasis
PTH and VitD
What kind of hormone is vitamin D?
Steroid hormone (any hormone derived from cholesterol)
What are the 2 forms of vitamin D?
Vitamin D2 - ergocalciferol (plants)
Vitamin D3 - cholecalciferol (humans).
When measuring vitamin D levels, which form of vitamin D is detected?
25-hydroxycholecalciferol
Outline the process of vitaminD synthesis
7-dehydrocholesterol + UVB–> cholecalciferol –> 25-hydroxycholecalciferol (liver 25-hydroxylase enzyme) –> activated by 1a-hydroxylase (under PTH control) –> 1,25-dihydroxycholecalciferol (Calcitriol)
What three elements is bone a reservoir of?
Calcium
Phosphate
Magnesium (important in the synthesis of PTH)
Radiological feature of osteomalacia
Looser’s zones (pseudofractures)
Features of rickets
Bowing of legs
Costochondral swelling
Myopathy
Widened epiphyses at the wrist
Whcih class of drugs induce the breakdown of vitamin D?
Anticonvulsants e.g. phenytoin
Why do chappatis cause vit D deficiency?
Contain a high level of phytic acid which chelates vitD in the gut and reduces absorption
Diagnosis of osteoporosis
T-score (
Example of a SERM
Raloxifene
What is the commonest cause of hypercalcaemia?
Primary hyperparathyroidism
How does the parathyroid gland detect calcium levels?
Through the CaSR
Name of condition with mutation in CaSR
Familial hypocalcuric/benign hypercalcaemia (AD)
Outlline brief pathophys of FHH/FBH
CaSR mutation, loss of sensitivity to calcium levels, higher setpoint for PTH release, mild hypercalcaemia, reduced urine Ca
Clinically normal as all bodily receptors do not detect calcium
3 types of hypercalcaemia in malignancy
Humoral hypercalcaemia of malignancy (PTHrp e.g. SCLC)
Bone mets e.g. breast Ca
Haematological malignancy e.g. myeloma
Which drug activates CaSR?
Cinacalcet acid
