Updated: 12/30/2021

Parathyroid Physiology

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  • Introduction
    • The parathyroid glands secrete parathyroid hormone (PTH)
      • PTH helps to maintain homeostasis of serum calcium and serum phosphate
      • secreted by the chief cells of the parathyroid glands
    • Anatomy
      • the parathyroid glands are 4 small glands, < 1 cm in diameter, located immediately posterior to the thyroid gland
      • usually located left superior, left inferior, right superior, right inferior
    • Regulation
      • primarily regulated by serum calcium in a negative feedback loop
        • calcium is sensed by the parathyroid glands' extremely sensitive calcium-sensing receptor (CaSR)
        • ↑ serum calcium results in ↓ PTH secretion
        • ↓ serum calcium results in ↑ PTH secretion
      • severe hyperphosphatemia will also result in ↑ PTH secretion
  • Parathyroid Hormone
    • Target organs
      • PTH ultimately has effects on three organs
        • bone
        • kidney
        • gut
    • Effects
      • net result is to ↑ serum calcium and ↓ serum phosphate
        • mnemonic - Phosphate-Thrashing Hormone
    • Physiologic Effects of Parathyroid Hormone
        • By Target Organ
        • Target Organ
        • Effect
        • Bone
        • ↑ Bone resorption of calcium and phosphate
        • Kidney
        •  Conversion of calcidiol (25-OH vitamin D) to calcitriol (1,25-(OH)2 vitamin D)
        •  ↓ Calcium excretion
        •  ↑ Phosphate excretion
        • Gut
        • ↑ Calcium and phosphate absorption in the small intestines
        • due to th↑ calcitriol
  • Related Clinical Conditions
    • Hypoparathyroidism
    • Hyperparathyroidism

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