What mechanism is primarily involved in mediating hypoparathyroidism leading to hypocalcemia?

Hypoparathyroidism leads to hypocalcemia primarily due to insufficient secretion of parathyroid hormone (PTH). PTH is crucial for maintaining calcium balance in the body, as it helps regulate calcium levels by acting on the bones, kidneys, and intestines.

When PTH is secreted, it stimulates the release of calcium from bones into the bloodstream, promotes renal reabsorption of calcium (reducing its loss in urine), and enhances the intestinal absorption of calcium (often mediated by increased activation of vitamin D). In cases of hypoparathyroidism, the decreased levels of PTH result in a failure to mobilize calcium from these sources, leading to lower serum calcium levels – a condition known as hypocalcemia.

While renal calcium reabsorption and gastrointestinal absorption are affected in different ways due to alterations in PTH levels, it is the lack of PTH itself that initiates the cascade of events resulting in reduced serum calcium. Therefore, the primary mechanism by which hypoparathyroidism causes hypocalcemia is due to insufficient secretion of parathyroid hormone.