Calcium Homeostasis Flashcards
how is the blood clotting ability of calcium utilised clinically
anti calcium agents are used to line the sample tube to prevent blood samples from clotting
where is 99% of the body’s calcium
in bone as hydroxyapatite
what percentage of calcium in the body is free and physiologically active
0.05%
purpose of calcium in cell signalling
their entry and exit into the cell triggers release of hormones (as in B cells for insulin) or neurotransmitters
5 roles of calcium
- signalling
- blood clotting
- apoptosis
- skeletal strength
- membrane excitability
how does calcium produce membrane excitation
RCMP is produced by Na+/K+ movement. Calcium decreases Na+ permeability and reduces excitability
which of the mentioned 5 roles of calcium is most critical to maintain homeostasis of an why
membrane excitability: if nerves/cells become hyperactive or underactive then chaos
what state of calcium (hyper/hypo) will cause Na+ permeability in neurons to increase (i.e. hyperexcitation) and what is the clinical consequence
HYPOcalcaemia. results in tetany. If this tetany spreads to the chest wall muscles and larynx it can results in asphyxiation
cardiac arrhythmia can be triggered by what state of calcium (hyper/hypo)
HYPERcalcaemia. decreased neuronal Na+ permeability –> reduced excitability –> depressed neuromuscular activity
what % of body calcium is stored intracellularly for things like muscle contraction
0.9%
normal calcium range in plasma (i.e. ECF)
2.2-2.6mM
How is the 0.1% calcium in plasma distributed
10% complexed to anion, 40% protein bound, 50% free
how does alkalosis increase the amount of calcium bound to proteins
fewer H+ ions –> fewer H+ to bind to proteins –> more spaces on proteins to bind to –> Ca2+ binds to spaces on protein
which situation has more protein bound calcium, alkalosis or acidosis
alkalosis
true/false calcium in bone will be released if Ca2+ levels in plasma are not sufficient
true - osteoclasts secrete H+ to dissolve the hydroxyapatite
what cells build up bone
osteoBlasts. they lay down a collagen matrix which is then calcified. It is this matrix that calcium is taken from
the two key hormones of raising calcium content in blood
parathyroid hormone and calcitrol
what vitamin is calcitrol derived from
vitamin D3
3 main sites of PTH action
bones, renal tubules and kidneys themselves
Ca2+ raising action of PTH on bone
stimulating osteoclasts
inhibiting osteoblasts
i.e. more breakdown, less deposition
action of PTH to raise Ca2+ in kidneys
increase renal excretion of phosphate, so it can’t join back up with calcium to form hydroxyapatite.
stimulate kidneys to make calcitriol from vit D
how does PTH raise Ca2+ by acting on the renal tubules
by increasing reabsorption of Ca2+ i.e. not be peed out
calcitriol formation is stimulated by what hormone in lactating women
prolactin
how does calcitriol increase gut Ca2+ absorption
by increasing expression for calcium transporters in gut
2 stimuli of calcitriol formation
prolactin and PTH
where do we acquire vitamin D from
from diet and from cholesterol precursors activated by UV light
vitamin D is fat/water soluble?
fat soluble
what hormones decreases plasma Ca2+
calcitonin
3 calcium raising action of calcitriol
- increased absorption in gut
- renal absorption
- stimulating osteoclasts
why might prolactin increase Ca2+
because lactating women have an increased demand for calcium as they are producing milk
effect of reduced vitamin D on bones
less calcitriol produced –> less Ca2+ from gut and kidneys –> PTH works harder –> more phosphate excreted –> greater Ca2+ loss from bone –> weaker, softer bones –> rickets/osteomalacia
where is calcitonin secreted from
the thyroid gland
what stimulates calcitonin release
raised blood calcium
2 calcium lowering actions of calcitonin
- inhibit osteoclasts
2. increase renal excretion of Ca2+
true/false excess calcitonin causes hypocalcaemia
false - its effects are overridden by PTH being stimulated by the low calcium levels produced
what hormone might be useful to treat Paget’s disease (overactive osteoclasts)
calcitonin –> it inhibits osteoclasts
