CALCIUM METABOLISM

CALCIUM METABOLISM

  • 9-11 mg/dl in plasma
  • 1-1.5 kg in a 70 kg healthy man out of which 50% is free, diffusible and ionized. Remaining 50% is bound.
  • Out of the bound fraction , 40% is bound to proteins which is non-diffusible and 10% to phosphate/citrate which is diffusible.
  • Also, out of the total Calcium 99% is in bones.
  • In bones and teeth (as hydroxyapatite)
  • For muscle contractions
  • Nerve impulse transmission
  • Blood coagulation
  • Activation of enzymes (direct or through calmodulin)
  • Second messenger
  • Regulation of exocytosis and endocytosis
  • Contact inhibition
  • Increases heart contraction vigor (prolongs systole)

Average adult

0.8 g/day

Pregnant/Lactating women

1.5 g/day

Children

0.8 – 1.2 g/day

Infants

0.3 – 0.5 g/day

  • BEST – Milk
  • OTHER – Beans, leafy vegetables, fish , egg yolk.
  • Promoting factors

Inhibiting factors

Vitamin D, PTH

Phytates , oxalates

Lactose , Lysine , Arginine

Free fatty acids

Acidic pH

Alkaline pH

  1. Calcitriol
  • Active form of Vit.D
  • It causes the synthesis of a specific calcium binding protein in the intestinal cells
  • This protein increases the calcium absorption from the gut
  • Also calcitriol stimulates calcium uptake by the osteoblasts of bone and promotes calcification
  1. PTH
  • It is original is synthesized as a pre hormone which is finally converted into active hormone.
  • PTH activates adenylate cyclase and this causes conversion of ATP into cAMP. This through its biological effects causes increase in intracellular calcium.
  • It causes demineralization of the bones which is a process carried out by osteoclasts.
  • It causes increase in calcium reabsorption from the kidney tubules and also promotes the production of calcitriol.
  • As it increases the production of calcitriol it also increases the intestinal absorption of calcium.
  1. Calcitonin
  • It is secreted by the parafollicular cells also called as the C Cells of Thyroid gland.
  • Its functions opposite to PTH , by promoting bone calcification and thus decreasing blood calcium level.
  • Out of the total Calcium excreted , 90% is through feces and 10% through urine.
  • Renal threshold for calcium is 10 mg/dl.
  • HYPERCALCEMIA – high PTH , low Phosphate levels, high ALP . Renal stones also observed.
  • HYPOCALCEMIA – low PTH. Tetany observed.
  • RICKETS/OSTEOMALACIA – usually due to Vit. D deficiency. High ALP observed.
  • RENAL RICKETS – Vit. D deficiency due to impairment in Renal tissues.
  • OSTEOPOROSIS – due to deficiency of Calcitriol production (seen in steroid hormone deficiency, because steroid hormone leads to calcitriol synthesis)
  • OSTEOPETROSIS – pathologically increased bone density 

-Prajwal Shetty

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