The parathyroid glands are endocrine glands located in the anterior neck, posterior to thyroid

They are responsible for the production of parathyroid hormone (PTH), which acts to increase the level of serum calcium.

• Neurovascular supply

2 cell types

• Chief cells– secrete parathyroid hormone.
• Oxyphil cells– larger but less abundant. purpose unknown. number increases with age, few are seen before puberty.

Parathyroid Hormone Synthesis

<aside> 💡 rough endoplasmic reticulum of chief cells make pre-pro-PTH → cleaved → pro PTH → cleaved → PTH → stored in granules

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Parathyroid Hormone Actions

• increase calcium levels in the body;
  • Increased bone resorption
    • acts on bone to increase bone resorption. It induces cytokine secretion from osteoblasts that act on osteoclast cells to increase their activity.
    • Increased bone breakdown → release Ca2+ and PO4- → bind together and go to kidney (but net increase serum, Ca2+)
  • Increased reabsorption in the kidney
    • increases Ca2+ absorbed from the Loop of Henle and distal tubules (mechanism is understood).
    • inhibits PO4 reuptake → increased excretion (important to prevent formation of calcium phosphate kidney stones).
  • Vitamin D synthesis- stimulates the formation of vitamin D, which subsequently increases absorption from the gut.

Parathyroid Hormone Regulation