Calcium Homeostasis Flashcards
What has 99% of our calcium?
bones
where is 0.1% of our calcium?
extracellular
where is 0.9% of our calcium?
mitochondria and sarcoplasmic reticulum
nearly half of calcium found in the ECF is bound to ….
protein
Where is the other half of calcium in the ECF (the half that is not bound to protein)
free in solution
physiologically active
how much (value) calcium is found in plasma?
2.2-2.6mM
What does calcium have a high affinity for?
proteins
small positive charge to large negative charge
Physiologically active Calcium in the plasma accounts for about 50% of plasma calcium. Therefore its value is approx
1.2mM
binding capacity of plasma proteins changes with what?
pH
binding capacity of plasma proteins increases under what conditions?
alkalotic
what happens to pH if you hyperventilate?
rises
alkalosis
What happens (with regards to calcium) when pH rises?
More proteins bind the calcium precipitating hypocalcaemia
In acidosis, plasma protein binding capacity is reduced therefore
free calcium in the plasma rises
bone will release calcium to maintain what plasma level of calcium?
1.2mmol
what are the two key hormones that act to increase calcium in the plasma?
parathyroid hormone
calcitriol
what is calcitriol?
active from of vitamin D3
Why cant you have your parathyroid glands removed?
you lose your ability to control calcium homeostasis
Parathyroid hormone is released in response to what?
low calcium in plasma
what effect does vitamin D3 have on plasma calcium?
increases it
what does vitamin D3 complement the actions of?
parathyroid hormone
when calcium plasma is low - and increase in PTH leads to an increase in ………. - which leads to increased ……. ……….. .. …….
calitriol
intestinal absorption of calcium
increase in levels of calcium inhibits
PTH
What three major processes do calcitriol binding to nuclear receptors regulate?
increases absorption of Ca from gut
facilitates renal absorption of Ca
Mobilises calcium stores in bone by stimulating osteoclast activity
Vitamin D3 acts to increase ………..
plasma calcium
Vitamin D deficiency - PTH maintains plasma Ca by taking Ca from
bones
rickets/ oestomalacia
vitamin D3 deficiency will result in reduced …… as well as …….
calcium
phosphate
