disorders of calcium and phosphate mechanism Flashcards
where do the lower parathyroids develop from?
the third pharyngeal arch
where do the superior parathyroids come from?
the fourth pharyngeal arch
what is the process of vitamin D production?
- 7-dehydrocholestrol in skin is converted to cholecalciferol after exposure to sunlight
- this travels to the liver and is converted into 25 OH vitamin d
- this goes to kidneys and is converted to 1, 25 di OH vitamin d.
What is the primary action of vitamin D?
to increase calcium reabsorption in the gut
what are the actions of PTH?
- increase vitamin d
- acts on bone to stimulate osteoblasts to express RANK ligand - osteoclasts
- increase calcium reabsorption in kidney and decrease phosphate reabsorption
what happens when there is too much calcium in the system? (2)
inhibition of 1 - alpha hydroxylation of vitamin D
production of calcitonin
high PTH causes?
hyperparathyroidism
cancer
low PTH causes
excessive vitamin D levels due to:
exogenous
granulomatous disease
William’s syndrome
what are the three classes of hyperthyroidism?
primary - ^ PTH and ^ calcium
secondary - ^ PTH and low C
teritiary - ^ PTH and ^ C
what do bone scans measure
osteoblast activity
what form of cancer cannot be picked up by bone scans
myeloma - directly stimulates osteoclasts and goes past osteoblasts
what are granulomas and what do they contain?
contain macrophages: 1 - alpha hydroxyls (enzyme that activates vitamin D)
what is familial hypercalciuric hypercalcaemia
raised PTH and calcium, but little calcium getting into urine.
defect in the calcium sensing gene (CaSR gene)
however asymptomatic and so leave it alone
if you suspect hypercalcaemia what do you look at?
calcium, phosphate, vit D, PTH and urinary calcium excretion.
