ONCB Metabolic/Inflammatory/Tumors Practice Test – Prep & Study Guide

The hormone primarily responsible for regulating calcium levels in the blood is parathyroid hormone. This hormone, produced by the parathyroid glands, plays a crucial role in maintaining calcium homeostasis in the body. When blood calcium levels drop, parathyroid hormone is released to promote several actions: it increases calcium reabsorption in the kidneys, enhances the release of calcium from bones into the bloodstream, and stimulates the conversion of vitamin D into its active form, which in turn enhances intestinal absorption of calcium. Through these actions, parathyroid hormone effectively raises blood calcium levels.

In contrast, while calcitonin can lower blood calcium levels by inhibiting osteoclast activity in bones and increasing calcium excretion in the kidneys, it plays a secondary role compared to parathyroid hormone. Growth hormone is primarily involved in growth and metabolism, rather than direct regulation of calcium levels. Cortisol, a glucocorticoid hormone, involved in metabolism and stress response, does not have a primary role in the regulation of calcium but can affect bone metabolism and the body’s overall calcium balance indirectly.