Calcium and phosphate regulation Flashcards
What is the major store of calcium?
bone (>95%)
what are the main types of stores of calcium?
inorganic minerals- calcium hydroxyapatite (65%)
organic components- Type I collagen (35%)
what is the initial precursor to calcitriol?
vitamin D
goes into the liver
what is the product created by the liver after vitamin D uptake?
calcidiol (25-OH-D)
inactivate form of vitamin D
where does calcidiol go next?
kidney
what is formed in the kidney from calcidiol?
calcitriol (1,25(OH)2D)
active form of vitamin D
where does calcitriol have its effects?
kidney
bone
small intestine
What is the effect of calcitriol in the bone?
increase release of calcium and phosphates
done by PTH also
what is the effect of PTH on the kidney?
increase in calcitriol synthesis
increased calcium reabsorption
increased phosphate excretion in urine
aim to retain calcium
what is the effect of calcitriol in the gut?
increase absorption of dietary calcium (and phosphate alongside it)
what is the effect of hypercalcaemia in terms of membrane excitability?
decreases excitability
due to blockage of Na+ (decreased Na+ influx)
what is the effect of hypocalcaemia in terms of membrane excitability?
greater influx of Na+ possible so excitability increases
what are the symptoms of hypocalcaemia?
o Parathesia. o Convulsions. o Arrhythmias. o Tetany. o Signs
what are the signs displayed in hypocalcaemia?
Chvostek’s sign – tap facial nerve below zygomatic arch, face twitch.
Trousseau’s sign – inflate BP cuff for minutes induces carpopedal spasm.
what are the causes of hypocalcaemia?
Vitamin D deficiency – low calcitriol.
o Renal failure – impaired 1alpha-hydroxylase activity therefore low calcitriol.
o Low PTH levels – hypoparathyroidism from neck surgery or autoimmune.
o PTH resistance – Pseudohypoparathyroidism.
