Blood calcium level is regulated in part by , a hormone secreted by the thyroid gland when the blood calcium level rises.

The hormone that regulates blood calcium level, secreted by the thyroid gland when the blood calcium level rises, is called Calcitonin. Here are the steps of how it works:

1. When the blood calcium level rises above the normal range, the thyroid gland detects this change.

2. In response, the thyroid gland secretes the hormone calcitonin.

3. Calcitonin has several effects on the body, all of which work together to decrease blood calcium levels.

4. It inhibits the activity of osteoclasts, cells that break down bone to release calcium into the blood.

5. It also increases the activity of osteoblasts, cells that build bone, thereby storing more calcium in the bones.

6. In addition, calcitonin reduces the reabsorption of calcium by the kidneys, leading to more calcium being excreted in the urine.

7. As a result of these actions, the level of calcium in the blood decreases back to the normal range.

8. When the blood calcium level is back within the normal range, the thyroid gland reduces the secretion of calcitonin.

This is a continuous and dynamic process that helps to maintain the balance of calcium in the body.