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.
| Inhibiting factors |
Vitamin D, PTH | Phytates , oxalates |
Lactose , Lysine , Arginine | Free fatty acids |
Acidic pH | Alkaline pH |
- 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
- 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.
- 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