Hypercalcemia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Pathophysiology

Mineral Homeostasis

The effect of parathyroid hormone on mineral metabolism is as follows: Effect of minerals and vitamin D on parathyroid hormone:

• Decrease in serum calcium concentration stimulates parathyroid hormone.
• Calcium provides negative feedback on parathyroid hormone.
• Magnesium provides negative feedback on parathyroid hormone.
• Vitamin D decreases the concentration of parathyroid hormone.
• Effect on parathyroid hormone on calcium metabolism:
  • Direct effect:
    • Increased resorption of bones.
    • Decreases excretion from kidney.
  • Indirect effect:
    • Increases conversion of inactive 25-hydroxy vitamin D to the active 1,25-dihydroxy vitamin D which increases absorption of calcium from gut. Decreased phosphate concentration also increases this conversion process. Vitamin D shows synergism with parathyroid hormone action on bone.
    • Decreased serum inorganic phosphate concentration prevents precipitation of calcium phosphate in bones.
  • Both these direct and indirect mechanism results in an increased serum calcium concentration.
• Effect of parathyroid hormone on inorganic phosphate metabolism:
  • Increases excretion of inorganic phosphate from kidney resulting in decreased serum concentration of phosphate.
• Effect of parathyroid hormone on magnesium concentration:
  • Decreases excretion of magnesium resulting in increased serum magnesium concentretion.

The Sequence of Events in Mineral Homeostasis

Parathyroid hormone

Kidney

Bone

Decreased excretion of magnesium

Increasead conversion of inactive 25-hydroyx vitamin D to the active 1,25-dihydroy xvitamin D

Increase excretion of inorganic phosphate

Decrease excretion of calcium

Increased resorption of bone

Increased serum concentration of magnesium

Increased absorption of calcium from gut

Decreased serum concentration of inorganic phosphate

Prevents precipitation of calcium phosphate in bones

Increased serum concentration of calcium