Calcium ions play a major role in many physiological events. A decline in blood calcium levels is regulated primarily by parathyroid hormone (PTH) released by the parathyroid gland. PTH stimulates...

Calcium ions play a major role in many physiological events. A decline in blood calcium levels is regulated primarily by parathyroid hormone (PTH) released by the parathyroid gland. PTH stimulates certain bone cells to break down bone, the small intestine to absorb more calcium from the diet, and the kidneys to reabsorb more calcium from the blood. As a result of these actions, blood calcium levels rise, and PTH release is then inhibited.

a. List three organ systems involved in the maintenance of blood calcium levels, and state the role of each organ system in the process. ___________________________________________________

b. Is blood calcium regulation an example of negative feedback control or positive feedback

control? Explain. ___________________________________________________________________