Session 11 - Lecture 1 - Calcium Metabolism Flashcards
1 - Parathyroid Gland
Parathyroid Gland
Calcium and Phosphate Regulation
{Intro to physiology of parathyroid gland and role in calcium regulation - will also touch on phosphate regulation - two do have interdependency with parathyroid hormone.}
2 - Calcium
Calcium (metal ion)
• Adult human contains ~1000 g of calcium
• 99% is sequested in bone in the form of hydroxyapatite crystals (Ca10(PO4)6(OH)2)
• Skeleton provides
– structural support
– major reserve of calcium
– Helps to buffer serum levels
– Releasing calcium phosphate into
interstitium
– Up taking calcium phosphate
• ~300-600 mg of calcium is exchanged between bone and ECF each day
- Diet 1000 mg/day
- Gut
- Feces 825 mg/day
- Absorbed 500 mg/day
- ECF 1000 mg (8.8-10.6 mg/dl)
- Secreted 325 mg/day
- Formation 280 mg/day
- Bone 1000 g
- Resorption 280 mg/day
- Filtered 10,000 mg/day
- Kidneys
- Reabsorbed 9825 mg/day
- Urine 175 mg/day
{So, PTH, Ca regulation, the role and the control of serum calcium.
Ca rly important – vital ion in our circulation – in our serum - regulation is v tightly controlled.
Vast majority of Ca (99%) sequestered into our bones. Formed in mineral form called hydroxyapatite – Ca bound up in crystal – deposited on collagen fibres and held in bones.
Skeleton rly important –
- physical role
- acts as a buffer – dynamic – as long as we remember bone is a living structure – Ca coming in and out of bone all the time – dynamic reservoir. 4. As well as release of Ca from hydroxyapa – also get P released – reservoir for P.
300-600 mg of Ca is moving in and out of our skeleton – not fixed, v dynamic.
Daily intake from diet (UK = 1000 mg/day)
Urinary loss 175 mg/day
GI loss 825 mg/day}
3 - Plasma calcium levels
Plasma calcium levels
- Serum calcium 2.2-2.6 mM
- ECF [Ca2+] a very small fraction of total-body calcium (>1% )
- Distributed among three interconvertible fractions
- Biologically active free ionized [Ca2+] closely regulated to 1.0-1.3 mM
- Most of the calcium in the body is stored in skeleton
Only free calcium is biologically active form!
Calcium (mg/dL 1 dL = 100 ml) Total calcium (Ca) 8.8 - 10.6 Ionised Ca 4.7 Protein bound-Ca 4.8 Complexed Ca (phosphate, citrate, etc) 0.6
Ca2+ 50%
Ca-Proteins 41%
Ca-X 9%
Ionized Ca 47%
Protein Bound Ca 47%
Complexed Ca (Pi, citrate etc) 6%
{Plasma calcium levels - routinely measured – v important – causes huge no of problems if serum calcium lvls move from v tightly bound amount.
Serum calcium, amount being measured is tiny fraction of that totality – 99% of ca bound up in our bones – only about 1% is that serum calcium.
Biologically active form of Ca – pie chart to show, just the ECF calcium – serum calcium – ionised portion of Ca, but then we can see there’s nearly same amount of calcium in ECF which is bound to proteins. And then we have another portion that is complexed to citrate and other acids. 3 fractions are all interconvertible – they move in an eqm.
The free Ca, ionised Ca only bit that causes biological effect – rest is there measured in serum calcium, but only active free ionised calcium that is biologically active}
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