Calcium plays a very important role in the formation of bones. Write on the role of endocrine glands and hormones responsible for maintaining calcium homeostasis.

Explanation

Calcium level of blood is regulated by two antagonistic hormones, thyrocalcitonin (TCT) of thyroid and parathormone (PTH) of parathyroids. TCT is hypocalcaemic factor and is secreted when `Ca^(++)` level of blood is higher than the normal level. TCT brings `Ca^(++)` level to normal by: Increasing deposition of `Ca^(++)` in the bone by activating osteoblasts, and increasing loss of `Ca^(++)` in urine by decreasing its reabsorption from the nephrons of the kidneys.
Conversely, PTH is a hypercalcaemic factor and is secreted when `Ca^(++)` level of blood is lower than the normal level. PTH brings `Ca^(++)` level to normal by: Increased bone resorption by activating osteoclasts, increasing absorption of `Ca^(++)` from intestine and decreasing `Ca^(++)` loss in urine by increasing reabsorption of `Ca^(++)` from the nephrons of the kidneys.