II. Physiology

  1. Images
    1. calciumHomeostasis.png
  2. Calcium is the most common mineral found in the human body
    1. Bones and Teeth
    2. Metabolic processes
      1. Enzyme modulator (when bound to calmodulin)
    3. Neuromuscular Function and Nerve Impulses
    4. Blood Clotting Pathway
    5. Cell Movement
  3. Total body Calcium distribution
    1. Skeleton: 98%
    2. Circulating: 2%
      1. Free or ionized Serum Calcium (active): 50%
      2. Albumin-bound Serum Calcium (inactive): 50%
  4. Parathyroid Hormone (PTH) modulates Serum Calcium (via Activated Vitamin D)
    1. PTH promotes renal activation of Vitamin D to 1,25-dihydroxycholecalciferol (activated Vitamin D)
      1. Calcium intestinal absorption is directly increased by 1,25-dihydroxycholecalciferol
        1. Intestinal Calcium absorption is the primary mechanism for regulating body Calcium
      2. Bone resorption increases with 1,25-dihydroxycholecalciferol
      3. Renal Distal convoluted tubule Calcium reabsorption increases with 1,25-dihydroxycholecalciferol
    2. PTH levels rise and fall inversely with Serum Calcium
      1. PTH rises in response to Low Serum Calcium (Hypocalcemia)
      2. PTH falls in response to High Serum Calcium (Hypercalcemia)
    3. PTH inhibits renal phosphate reabsorption
      1. Serum Phosphate would typically rise with Calcium reabsorption in gut, Kidneys and with bone resorption
      2. However, PTH's inhibition of renal phosphate reabsorption prevents Hyperphosphatemia
  5. Vitamin D effects vary by concentration
    1. Low concentrations of Vitamin D
      1. Promotes bone calcification
      2. Increases Calcium gastrointestinal absorption and renal reabsorption
      3. Persistent Vitamin D Deficiency may result in Rickets
    2. High concentrations of Vitamin D
      1. Functions in similar way to Parathyroid Hormone
      2. Increases bone resorption
  6. Other factors affecting Calcium levels (less significant than PTH and Vitamin D)
    1. Calcitonin
      1. Calcitonin increases bone mineralization
      2. Calcitonin decreases Serum Calcium
    2. Blood pH
      1. Acidosis promotes Hypercalcemia
        1. Decreased Calcium plasma Protein binding (Calcium is displaced by excess Hydrogen Ion)
      2. Alkalosis promotes Hypocalcemia
        1. Increased Calcium plasma Protein binding
        2. Hyperventilation (and associated alkalosis) may result in transient Tetany from Hypocalcemia

III. Associated Conditions

IV. References

  1. Goldberg (2014) Clinical Physiology, Medmaster, Miami p. 31

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