Calcium and Bone Flashcards
What are the roles of calcium in the body?
Hormone secretion, nerve conduction, activation and inactivation of enzymes, muscle contraction and exocytosis, intracellular signalling pathways, eases insomnia
What is the range for calcium levels in the blood plasma?
1.0 - 1.3 mM or 4.0 - 5.2 mg/dl
What forms does calcium exist as in blood plasma?
Free ionised species, bound to or associated with anionic sites on serum proteins (especially albumin), complexed with low-molecular-weight organic anions
How are calcium and phosphate homeostasis linked?
Both are major components of hydroxyapatite crystals in bone, regulated by the same hormones - PTH and calcitriol (1,25-dihydroxyvitamin D)
What do PTH and calcitriol do?
Raise serum calcium concentrations. Calcitonin lowers serum calcium and preserves maternal skeleton in pregnancy.
Describe hormonal regulation of serum calcium
Chief cells have G protein calcium receptors, when Ca2+ binds it stimulates phospholipase C which inhibits adenylate cycles leading to reduced cAMP and reduced PTH
Where does vitamin D2 come from?
Absorption by the gut
Where does vitamin D3 come from?
UV light on the skin
Where does calciferol come from?
Liver. It’s the produce of the first hydroxylation of vitamin D
Where does calcitriol come from?
Kidney. It’s the produce of the second hydroxylation of vitamin D
Explain the significance of renal function on calcium metabolism
PTH increases absorption of Ca2+ in distal convoluted tubule. Pi is removed from circulation by inhibition of proximal tubule reabsorption, preventing calcium stone formation
What does hypocalcaemia result in?
Hyper-excitability in NS, including NMJ leading to parasthesia, tetany, paralysis and even convulsions. Low amount of Ca2+ bound to NMJ therefore Na+ depolarises is much quicker
What does hypercalcaemia result in?
Kidney stones (renal caliculi), constipation, dehydration, kidney damage, depression and tiredness (moans, stones and groans)
What can excess PTHrP indicate?
Cancerous tumour - humeral hypercalcaemia of malignancy.
How is calcium absorbed?
In the small intestine - active process
