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How do the parathyroid glands detect changes in blood calcium levels?

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human endocrine system The principal glands of the female and male human endocrine systems.

The parathyroid glands detect changes in blood calcium levels through specialized calcium-sensing receptors located on the surface of their cells.1

These receptors function as a regulatory mechanism for the secretion of parathormone (PTH) based on the concentration of ionized calcium in the blood:1

When blood calcium levels decrease: There is less binding of calcium to the receptors on the parathyroid cells. This reduction in binding triggers an increase in the secretion of PTH.1
When blood calcium levels increase: More calcium binds to these receptors, which signals the cells to decrease or inhibit the secretion of PTH.1

This process operates via a negative feedback loop, ensuring that serum calcium concentrations are maintained within a normal range to support vital physiological functions, such as muscle contractility and nervous system excitability.12