Major Mediators of Calcium and Phosphate Balance
Parathyroid hormone (PTH)
Calcitriol (active form of vitamin D3)

Role of PTH
Stimulates renal reabsorption of calcium
Inhibits renal reabsorption of phosphate
Stimulates bone resorption
Inhibits bone formation and mineralization
Stimulates synthesis of calcitriol

Role of Calcitriol
Stimulates GI absorption of both calcium and phosphate
Stimulates renal reabsorption of both calcium and phosphate
Stimulates bone resorption

Increased GI Absorption
    Milk-alkali syndrome
    Elevated calcitriol
        Vitamin D excess
            Excessive dietary intake
            Granuomatous diseases
        Elevated PTH
        Hypophosphatemia
Increased Loss From Bone
    Increased net bone resorption
        Elevated PTH
            Hyperparathyroidism
        Malignancy
            Osteolytic metastases
            PTHrP secreting tumor
    Increased bone turnover
        Paget’s disease of bone
        Hyperthyroidism
Decreased Bone Mineralization
    Elevated PTH
    Aluminum toxicity
Decreased Urinary Excretion
    Thiazide diuretics
    Elevated calcitriol
    Elevated PTH

Etiologies of Hyperphosphatemia
Increased GI Intake
    Fleet’s Phospho-Soda
Decreased Urinary Excretion
    Renal Failure
    Low PTH (hypoparathyroidism)
        s/p thyroidectomy
        s/p I131 treatment for Graves disease of thyroid cancer
        Autoimmune hypoparathyroidism
Cell Lysis
    Rhabdomyolysis
    Tumor lysis syndrome

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