What stimulates the removal of calcium from bones by osteoclasts?

The removal of calcium from bones by osteoclasts is primarily stimulated by parathyroid hormone (PTH), which is released by the parathyroid glands in response to low blood calcium levels. PTH increases osteoclast activity, leading to bone resorption and the release of calcium into the bloodstream. Additionally, factors such as vitamin D and certain cytokines can also enhance osteoclast activity and contribute to calcium mobilization from bones.