Calcium Homeostasis Flashcards
what is the role of calcium In the body?
> signalling > blood clotting > skeletal strength > membrane excitability > apoptosis
what is the effect of calcium on the permeability of membrane to sodium?
calcium decreases permeability
what is the effect of hypocalcaemia on the membrane excitability of neurons?
there is hyper-excitation (which can cause tetany)
how can hypercalcaemia cause cardiac arrhythmias?
there is a decrease in neuronal sodium permeability which reduces the excitability and depresses neuromuscular activity.
where is the intracellular calcium stored?
in mitochondria and sarcoplasmic reticulum
describe the calcium distribution in the body
> 99% is in bones
0.9% is in intracellular fluid
0.1% is in extracellular fluid
what percentage of calcium is bound to proteins?
40%
what is the normal extracellular calcium concentration in adults?
2.5mM
how much of the calcium is physically active (free ionised)?
1.2mM = 50%
if 50% ca is free ionised, 40% is protein bound where is the remaining 10% of extracellular calcium?
bound to plasma anions
true or false:
the binding capacity of calcium increases in alkalotic conditions
true
in hypoventilation how is the calcium concentration affected?
the plasma calcium decreases as the ph increases causing more calcium to bind to the plasma proteins
what is the function of osteoblasts?
they lay down collagen extracellular matrix and calcify it
what is the function of the osteoclasts?
they mobilise bone:
> secrete H ions (ph4) to dissolve calcium salts
> they provide proteolytic enzymes to digest extracellular matrix
what is the function of the osteocytes?
they regulate the activity of osteoblasts and osteoclasts
what do osteocytes differentiate from?
osteoblasts
what 2 hormones increase calcium conc. in the plasma?
> parathyroid hormone
> calcitriol
what produces calcitriol?
the liver and kidneys
true or false:
calcitriol is an active form of vitamin D3
true
what are the actions of the parathyroid hormone?
> stimulates osteoblasts
stimulates kidney to synthesise calcitriol
inhibits osteoblasts
increases calcium reabsorption from the kidney tubules
increases renal excretion of phosphate
how does the increased excretion of phosphate elevate free calcium?
it prevents it from being deposited back into the bone
what activates the formation of calcitriol?
prolactin
what are the actions of calcitriol?
> increased calcium absorption from the gut
mobilisation of calcium stores in the bone
facilitation of renal absorption of calcium (osteoclasts)
what is the effect of vitamin d deficiency?
since there is a decrease in calcium concentration in the plasma then to compensate calcium is removed from the bone causing osteomalacia and rickets
what conditions does vitamin d deficiency have implications in?
> MS
cancer
arthritis
CVD
what hormone decreases calcium conc.?
calcitonin
what gland produces calcitonin?
thyroid gland
true or false calcitonin is a steroid hormone?
false it is a peptide hormone
what are the actions of calcitonin?
> inhibits bone resorption by binding to osteoclasts
> increased calcium excretion
why does growth hormone affect calcium levels?
it is a constant stimulus for bone formation
what is the effect of cortisol on calcium balance?
> increases renal excretion
inhibits osteoblasts
reduces intestinal absorption of calcium
decreases calcium plasma = increased parathyroid hormone
what is the effect of insulin on calcium balance?
> increases bone formation
> antagonises cortisol
why is osteoporosis a major problem in menopause?
oestrogen has a role in promoting bone formation
