Calcitonin

Calcitonin is a hormone produced in parafollicular cells of the thyroid that participates in regulating the
blood level of calcium and stimulates bone mineralization. A synthetic preparation of the hormone is
used in the treatment of certain bone disorders. Calcitonin acts to reduce the blood level of calcium and
to inhibit bone resorption, whereas parathyroid hormone acts to increase blood calcium level and bone
resorption. Vitamin D also contributes to the regulation of calcium homeostasis.

Functions

– the main function of Calcitonin is to regulate the levels of calcium and phosphorous in the bodies of a variety of different animals. In its natural form, it helps prevent the body from taking up calcium from bones and from reabsorbing the mineral through the urinary tract. The actions of both these functions helps to decrease the amount of calcium in the bloodstream. For people with osteoporosis, Calcitonin is a medical supplement to prevent bone loss.   

Mechanisms

Calcitonin reduces calcium levels in the blood by two main mechanisms:

1. It inhibits the activity of osteoclasts, which are the cells responsible for breaking down
bone. When bone is broken down, the calcium contained in the bone is released into the
bloodstream. Therefore, the inhibition of the osteoclasts by calcitonin directly reduces the
amount of calcium released into the blood. However, this inhibition has been shown to be
short-lived.

2. It can also decrease the resorption of calcium in the kidneys, again leading to lower blood
calcium levels.
How Calcitonin is controlled?

The secretion of both calcitonin and parathyroid hormone is determined by the level of calcium
in the blood. When levels of calcium in the blood increase, calcitonin is secreted in higher
quantities. When levels of calcium in the blood decrease, this causes the amount of calcitonin
secreted to decrease too.

The secretion of calcitonin is also inhibited by the hormone somatostatin which is also released
by the C-cells in the thyroid gland.