Which hormone opposes the action of parathyroid hormone?

The hormone that opposes the action of parathyroid hormone (PTH) is calcitonin. Parathyroid hormone increases the concentration of calcium in the blood by promoting the release of calcium from bones, stimulating reabsorption of calcium in the kidneys, and enhancing the absorption of calcium in the intestines. In contrast, calcitonin, which is produced by the thyroid gland, functions to lower blood calcium levels. It achieves this by inhibiting the activity of osteoclasts, the cells responsible for bone resorption, and promoting the deposition of calcium into the bones.

By acting in opposition to parathyroid hormone, calcitonin plays a critical role in calcium homeostasis, ensuring that calcium levels remain balanced in the body. This mechanism is vital for various physiological processes, such as muscle contraction, blood clotting, and maintaining healthy bone structure.

The other hormones listed do not have a direct role in calcium regulation. Insulin primarily regulates glucose metabolism, adrenaline (epinephrine) is involved in stress responses and increases blood glucose levels, and cortisol is a glucocorticoid that primarily affects metabolism and immune responses. Therefore, they do not counteract the actions of parathyroid hormone in the way that calcitonin does