26 - Calcium Flashcards
Hypocalcinaemia
Causes irritable nerves
Why tachyarrhythmia in hypocalcinaemia
o Calcium stabilises Na+ channels so if not enough = reduces threshold for AP to fire –> tetany, tachyarrhythmias
Which cells in parathyroid gland secrete PTH
Chief cells
What dye do oxyphils take up
technetium
Effects of PTH
o BONE: PTH enhances Ca release from bones + phosphate ( don’t need more phosphate hence excreted by kidney)
o INTESTINE: Enhances the absorption of calcium and phosphate from the small intestine by activating 1,25D (calcitriol)
o KIDNEY: Decreases calcium excretion in urine and increases phosphate excretion in urine
Formation of pth
polypeptide prohormone preproPTH (RER) → proPTH (Golgi)→ PTH (Vesicles)
When is PTH released
When low serum calcium
o PTH 1-84 has a circulation life
2 minutes
Calcium sensing receptor
o GPCR – reduces PTH secretion → increases breakdown of stored PTH
Supresses transcription of PTH gene
Restrains PTH proliferation
Familial hypocalciuric hypercalcemia (FHH)
Changes set point of calcium
Calcitriol on PTH
Suppresses PTH gene transcription
Phosphate on PTH
Stimulates PTH gene transcription
Cinacalcet
activates the CASR and reduces calcium levels
Reabsorption in proximal tube
65% reabsorption – PTH independent (voltage gradient)
Reabsorption in loop of henle
% reabsorption – PTH independent - Loop diuretics inhibit- CASR downregulates Na/K/2Cl
Reabsorption in distal tubule
10% reabsorption – PTH upregulates Ca channels, calcium ATPase and Na/Ca exchanger, TPRV
Other renal PTH effects
o Down-regulation of NaPi transporters - Reduced phosphate reabsorption
o Vitamin D Activation
Stimulation of 25(OH) D3 –> 1,25(OH)2 D3
Function of opg
inhibits osteoclastogenesis
Bone made of
Collagen + Hydroxyapatite
when mineralised = + Phosphate and alkaline phosphate
What can inactivate vitamin D
hydroxylated at the 24
Vitamin D receptor
o Nuclear and membrane bound
o VDR inihibits 1 α hydroxylase (negative feedback)
FGF 23
hormone that reduces serum phosphate
o Activating mutation in FGF23 - Autosomal dominant hypophosphataemic rickets
o Tumour induced osteomalacia - paraneoplastic FGF23
o Familial tumoral calcinosis - low levels FGF23
Calcitonin prodiced
Thyroid C cells
Primary hyperparathyroidism
o Rugger Jersey Spine
o Terminal Tuft Erosion
o Brown tumour
What causes primary hyperparathyroidism
Parathyroid tumour
Primary hypercalcaemia
o Kidney stones o Osteoporosis o Mood disorder – depression o Diabetes- Polyuria and polydipsia o MIBI SCAN
Hypocalcaemia symptoms
o Convulsions
o Arrhythmia
o Tetany
o Kidney stones (both hyper and hypo)
Tx of hypocalcaemia
IV oral calcium
chronic - alfacalcidol (1,25 vitamin D3) orally – increase gut absorption of Ca but lack of PTH means Ca will be lost from kidneys at a high rate
