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How do the parathyroid glands maintain calcium levels in the blood?
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Endocrine system
The glands of the human endocrine system.
The parathyroid glands maintain blood calcium levels primarily by secreting parathyroid hormone (PTH) in response to low serum calcium concentrations, which are monitored by calcium-sensing receptors on the surface of parathyroid cells.12
PTH acts to increase blood calcium levels through three main mechanisms:
- Bone Mobilization: PTH stimulates osteoclasts to break down bone tissue, releasing stored calcium into the bloodstream.12
- Renal Reabsorption: It acts on the kidney tubules to enhance the reabsorption of calcium from the urine, preventing its excretion.32
- Intestinal Absorption: PTH stimulates the kidneys to activate vitamin D into its most active form, calcitriol. Calcitriol then travels to the small intestine, where it increases the efficiency of dietary calcium absorption into the blood.32
Additionally, PTH lowers serum phosphate levels by inhibiting its reabsorption in the kidneys, which helps prevent the formation of insoluble calcium-phosphate complexes and further supports the elevation of ionized calcium in the blood.32