Calcium Hameostasis Flashcards
What is normal range for calcium?
2.2-2.6 mmol/L
What are the roles of calcium in the body?
- Signalling
- Blood clotting
- Apoptosis
- Skeletal strength
- Membrane Excitability
What proportion of calcium is distributed in bone?
99%
What proportion of calcium is found in ICF?
0.9%
What proportion of total body calcium is found in extracellular fluid?
0.1%
What are the main forms which calcium exists in in blood?
- Bound to protein
- Ionised/Free
- Bound to anions
What proportion of calcium is bound to protein in blood?
40% - 80% albumin, 20% to globulin
What can alter the protein binding of calcium in blood?
pH
What does acidosis do to free calcium?
Increases free calcium as H+ displaces calcium
What does alkalosis do to free calcium levels in the blood?
Decreased plasma calcium due to increased binding sites on protein
What is the function of osteoblasts?
Bone building cells - lay down collagen ECM
What is the function of osteoclasts?
Bone mobilisation - secrete H+ to dissovle calcium salts and ezymes to digest ECM
What is the function of parathyroid hormone?
- Stimulates osteoclasts - release Ca2+ and phosphate in bone
- Inhibit osteoblasts
- Increase Ca2+ reabsorption at the kidneys - decreased excretion
- Increasing renal excretion of phosphate - elevates free Ca2+ by preventing it from being deposited back in bone
- Stimulates calcitriol synthesis by the kidneys from vitamin D3 - promotes calcium absorption at the gut and kidney
What is PTH released in response to?
Decreased free Ca2+
What senses fluctations in calcium levels?
Calcium sensing receptors - on parathyroid chief cells
Draw how calcitriol is produced
What are dietary sources of vitamin D?
- Fortified milk
- Egg
- Fish oil
What is the action of calcitriol?
- Increases absorption of Ca2+ from the gut - In low [Ca2+] situation, increase in PTH, which increases Calcitriol, which increases intestinal absorption
- Facilitates renal reabsorption of Ca2+
- Mobilises calcium stores in bone by stimulating osteoclast activity
What is calcitonin?
Peptide hormone produced by thyroid gland
What is the main function of calcitonin?
Its main actions are to bind to osteoclasts and inhibit bone resorption as well as renal excretion so preventing a further in Ca2+ .
How does cortisol affect calcium balance?
- Inhibits osteoblasts
- Increases renal excretion of Ca2+ and phosphate
- Reduces intestinal absorption of Ca2+ -> increased PTH -> increases bone resorption.
These factors together can, over time, produce osteoporosis.
How does insulin influence calcium balance?
- Increases bone formation
- Antagonisis the action of cortisol
What influence does oestrogen have on calcium balance?
Promotes bone formation via oestrogen receptors on osteoblasts
How does prolactin influence calcium balance?
Promotes absoprtion from the gut by stimulating calcitriol synthesis
How does growth hormone influence calcium balance?
Constant stimulus for bone formation
