Hyperparathyroidism

PTH Actions - Core Physiology

PTH raises serum calcium and lowers serum phosphate by:

• ↑ Bone resorption → ↑ Ca²⁺ and ↑ phosphate
• ↑ Activation of vitamin D → ↑ GI absorption of Ca²⁺ and phosphate
• ↑ Renal calcium reabsorption (DCT) → ↑ Ca²⁺
• ↓ Renal phosphate reabsorption (PCT) → ↓ phosphate (phosphaturia)
• Normal state: ↑ Ca²⁺, ↓ phosphate

Primary Hyperparathyroidism

• Hyperfunction of parathyroid cells due to hyperplasia, adenoma or carcinoma.
• ↑ PTH
• ↑ Ca²⁺
  • Kidney Ca²⁺ and bone resorption
• ↓ Phosphate
  • Kidneys waste phosphate

Secondary Hyperparathyroidism

• Stimulation of the parathyroid due to chronic low Ca
  • Chronic renal failure or low vitamin D (liver disease → can't convert Vit D into calcitriol)
• ↑ PTH
• ↓ Ca²⁺
  • ↓ 1-alpha hydroxylase (kidney) → ↓ active vitamin D → ↓ Ca²⁺ absorption from gut
• ↑ Phosphate
  • ↓ phosphate excretion by the kidney
  • Kidney can't remove phosphate -> binds to free Ca

Tertiary Hyperparathyroidism

• Autonomous parathyroid hyperplasia after long-standing 2ndary parathyroidism
  • Typically, in End Stage Renal Disease
  • Become autonomous and secrete PTH regardless of Ca levels
• ↑ ↑ PTH (unregulated)
• ↑ Ca²⁺
  • ↑ PTH
• ↑ Phosphate
  • Kidneys still can't excrete phosphate (↓ phosphate excretion)