What defines hypoparathyroidism?

Hypoparathyroidism is characterized by insufficient secretion of parathyroid hormone (PTH). PTH plays a crucial role in regulating calcium levels in the blood, maintaining bone health, and influencing the metabolism of phosphorus and vitamin D. When there is a decrease in PTH secretion, the result can be low calcium levels (hypocalcemia) and elevated phosphorus levels (hyperphosphatemia), leading to symptoms such as muscle cramps, seizures, and tingling sensations.

In this context, the condition specifically refers to the underproduction of PTH, which directly impacts calcium homeostasis. Therefore, the defining characteristic of hypoparathyroidism is indeed related to the insufficient secretion of parathyroid hormone, aligning with the fundamentals of endocrine function and balance.

The other options address unrelated facets: excess secretion of PTH pertains to hyperparathyroidism, while non-functional parathyroid glands do not accurately encapsulate hypoparathyroidism's definition since the glands could still produce some hormone. Lastly, asserting a total absence of calcium in the body does not reflect the clinical reality of hypoparathyroidism; instead, it leads to a state of imbalance rather than complete depletion of calcium.