Calcium Metabolism


Mnemonic: Six ‘C’s

  1. Contraction of muscles (Coupling of excitation-contraction)
  2. Conduction in nerves
  3. Cardiac function
  4. Coagulation in blood (Co-factor)
  5. Communication (intracellular messengers) for hormones, autacoids and transmitters
  6. Cementing (mineralization) of bone – Compressive strength


Average young adult = 1200 gm calcium

  • 99% in bone as calcium hydroxyapatite
  • 1% in body fluids bone
    • 1% in ECF
      • 50% freely ionized (biologically active)
      • 40% protein bound (80% to albumin and 20% to globulin)
      • 10% complexed with small anions
    • 99% in ICF


Young children400-700 mg/day (2-3 dairy equivalents)
Adolescents and young adults (10-25 yrs)1300 mg/day (5 dairy equivalents)
Healthy adults (25-50 yrs)750 mg/day
Pregnant, Postmenopausal and Healing fracture1500 mg/day
Lactating2000 mg/day
Calcium metabolism
“Major interactions between vitamin D, parathyroid hormone (PTH), calcium and phosphorus around the body” by sportEX journals is licensed under CC BY-ND 2.0. To view a copy of this license, visit


Parathyroid hormone (PTH)Vitamin DCalcitonin
ProductionParathyroid chief cells 🡢 PTH
Negative feedback control by calcium
Diet/skin/UV 🡢 Vit. D3
Liver 🡢 25(OH) D
Kidneys 🡢 1,25(OH)2 D
Thyroid parafollicular C cells 🡢 Calcitonin
Positive feedback control by calcium
Intestine🡡 Calcium absorption
🡡 Phosphate absorption (Secondary PTH 🡢 Increased active vitamin D)
🡡 Calcium absorption
🡡 Phosphate absorption
Kidney🡣 Calcium excretion (DCT)
🡡 Phosphate excretion
🡡 1,25 (OH)2 D production (1-α-hydroxylase)
🡣 Calcium excretion
🡣 Phosphate excretion
🡡Calcium excretion
🡡 Phosphate excretion
BoneBinds to osteoblasts and upregulates RANKL 🡢 Activates osteoclasts 🡢 🡡 Calcium and phosphate resorption
Pulsed = anabolic; Continuous = catabolic
🡡 Calcium and Phosphate resorption [1,25(OH)2 D]
🡡 Bone formation [24,25(OD)2 D]
Inhibits osteoclasts 🡢 🡣 Calcium resorption
Net effect on serum levels🡡Calcium, 🡣Phosphate🡡Calcium, 🡡Phosphate🡣Calcium, 🡣Phosphate

1. There’s 1 liver – 1st hydroxylation of vitamin D occurs in liver (makes calcidiol)
2. There are 2 kidneys – 2nd hydroxylation of vitamin D occurs in kidneys (makes calcitriol)
3. PTH = Phosphate Thrashing Hormone

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