Which two hormones are primarily involved in the regulation of calcium levels in the blood?

The hormones that are primarily involved in the regulation of calcium levels in the blood are parathyroid hormone (PTH) and calcitonin.

PTH is secreted by the parathyroid glands in response to low blood calcium levels. It functions to increase blood calcium levels by promoting the release of calcium from bones into the bloodstream, enhancing the reabsorption of calcium by the kidneys, and stimulating the conversion of vitamin D into its active form, which increases intestinal absorption of calcium.

Calcitonin, on the other hand, is produced by the thyroid gland and has the opposite effect of PTH. It is released in response to high blood calcium levels and works to lower calcium levels by inhibiting bone resorption, which reduces the release of calcium from bones, and by enhancing the excretion of calcium through the kidneys.

The balance and interplay between these two hormones are crucial for maintaining calcium homeostasis in the body, ensuring that calcium levels in the blood remain within a narrow and safe range.