Calcium homeostasis Flashcards
when calcium is ionised it is inactive/active ?
when calcium is protein bound it is inactive/active ?
active
inactive
what is calcium bound to in bone
phosphates
what are the 3 hormones involved in calcium homeostasis
1,25-dihydroxyvitamin D
parathyroid hormone
calcitonin
where is parathyroid hormone produced
chief cells of parathyroid gland
parathyroid hormone responds to hyper/hypocalcaemia?
hypocalcaemia
what the pathway that involves the CaSR
calcium binds to CaSR activating PLC
PLC converts PIP2 into DAG + IP3
IP3 triggers release of Ca from SR/ER
what type of receptors are located on osteoblasts
PTH receptors
what is PTH responsible for
increasing extracellular Ca
how does PTH work on bone
stimulates cytokines that recruit osteoblasts that then induce osteoclasts
why are osteoclasts important in terms of Ca
help break down hydroxyapitie crystals
effect of PTH on small instestine
activates synthesis of 1,25-dihydroxyviamin D
effect of PTH on kidneys
increases Ca reabsorption by increasing activity of Ca pumps and channels
and increases phosphate excretion
where is 1,25-dihydroxyvitamin D (calcitriol) produced
kidneys
why are osteoclasts good for increasing Ca conc in blood
they break down bone to release phosphate and Ca into blood
what does 1,25-dihydroxyvitamin D do in the small intestine
diffuses into enterocytes where it binds to vitamin D receptors and increases gene expression
increases calcium absorption in small intestine
what are negative feedback of second hydroxylation
decrease in FGF23 and 1,25-dihydroxyvitamin D
1,25-dihydroxyvitamin D role in kidney
increases expression of Na-Pi cotransporters
improves PTH mediated Ca reabsorption
1,25-dihydroxyvitamin D role in bone
increases number of osteoclasts
where is calcitonin produced
clear cells of thyroid glands
calcitonin responds to
hypercalaemia
calcitonins role in bone
reduces rate of bone turnover and release of Ca from bone
calcitonins role in kidneys
increase Ca excretion
what do glucocorticoids regulate
bone density and intestinal Ca absorption
parathyroid related proteins
mimics actions of PTH
name the most studied phosphatonin
FGF23
FGF23 stimulates
phosphate loss in urine
How does FGF23 affect calcitriol (active vitamin D) production?
FGF23 decreases calcitriol production by inhibiting the enzyme 1α-hydroxylase in the kidneys
what does FGF23 prevent
hyperphosphatemia
what is hypocalcaemia
low plasma Ca
signs and symptoms of hypocalcaemia
pins and needles
muscle spasms
paralysis
convulsions
what happens to voltage gated Na channels when Ca is low
open at resting membrane potential
what is hypercalcaemia
high plasma Ca
signs and symptoms of hypercalcaemia
bones stones grones and psychiatric overtones
what is hypoparathyroidism
lack of PTH
signs and symptoms of hypoparathyroidism
hypocalcaemia
hyperphosphataemia
muscle spasms
what is hyperparathyroidism
excess of PTH
What can cause hyperparathyroidism
tumors
chronic kidney disease
calcium malabsorption
signs and symptoms of hyperparathyroidism
hypertension
consitpation
weakness
hypercalcaemia
confusion
severe vitamin D deficiency can cause
osteomalacia
rickets
