The hormones and endocrine glands that are responsible for maintaining calcium homeostasis, are thyroid and parathyroid glands and their associated hormones are calcitonin and Parathyroid Hormone (PTH).
(i) Parathyroid glands - These glands developed from the endoderm of the embryo. The cells of parathyroid glands are of two types - chief cells and oxyphil cells. The chief cells of the parathyroid glands secrete parathyroid hormone $(\mathrm{PTH})$.
This hormone (PTH) is involved in regulation of calcium and phosphate balance between the blood and other tissue. It mobilises the release of calcium into the blood from bones. PTH increases reabsorption of calcium by the body organs like intestine and kidneys.
(ii) Thyroid gland - It is the largest endocrine gland located anterior to the thyroid cartilage of the larynx in the neck. This gland plays a major role in maintaining calcium homeostasis. It releases thyrocalcitonin hormone produced by the parafollicular cells, also called, ' $\mathrm{C}$ ' cells.
This hormone is secreted when the calcium level in blood gets high. It is a 32 amino acid peptide hormone that lowers the calcium level bysuppressing release ofcalcium ions from the bones. Calcitonin thus has an action opposite to that of the parathyroid hormone in calcium homeostasis.