In response to high levels of blood calcium,

Parathormone (PTH) is a hypercalcemic hormone secreted by the parathyroid glands. Thyrocalcitonin (TCT) is a hypocalcemic hormone secreted by the parafollicular cells of the thyroid gland. These two hormones maintain calcium homeostasis. An increase in blood calcium levels stimulates the release of TCT while a decrease in blood calcium levels stimulates the release of PTH.