Updated: 6/1/2019

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 the calcitriol
 
Related Clinical Conditions
  • Hypoparathyroidism 
  • Hyperparathyroidism 

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