256. Calcium homeostasis Flashcards
What are the roles of calcium in the body?
Signalling
Blood clotting
Apoptosis
Skeletal strength
Membrane excitability
How does calcium affect the cell membrane?
Hypocalcaemia- hyperexcitation of neurones, tetanus
Hypercalcaemia- decreases neuronal sodium, arrhythmias
Where is calcium stored in the bodY?
Bones- 99%
Intracellular- 0.9%
extracellular- 0.1%
What other element is closely related in controlling calcium balance?
Phosphate
This is because in bone calcium is stored as hydroxyapatite, calcium and phosphate
What cells control how calcium is stored in bone?
Osteoblasts- build bone
Osteoclasts- cut bone away (mobilise calcium)
What two hormones cause calcium to be mobilised?
Parathyroid hormone- produced by parathyroid glands
Calcitriol- produced from vit D by liver and kidneys
How does parathyroid hormone increase free calcium?
Stimulates osteoclasts to increase absorption of calcium in bones
inhibits osteoclasts
increases kidney calcium reabsorbtion
Increases renal excretion of phosphate to allow more free phosphate
stimulates calcitiol synthesis
What are the actions of calcitriol?
Increase absorption of calcium from the gut
facilitates renal absorption of calcium
Mobilises calcium stores in bone by stimulating osteoclast activity
What hormone acts to decrease free caclium?
How does it work?
Produced by thyroid gland, secretion stimulated by decreases calcium in the plasma
Causes increased kidney loss
Not a very important hormone
What other hormones have a secondary effect at reducing calcium?
Cortisol
Insulin
Oestrogen
Growth hormone
