The next endocrine gland that we'll discuss is the parathyroid gland. The parathyroid glands
are 4-8 tiny, yellow brown glands that are embedded in the posterior surface of the thyroid.
They contain 2 types of cells, oxyphil cells in which the function is not really clear and
parathyroid cells which are going to secrete the hormone parathyroid hormone. Parathyroid
hormone is another important hormone in calcium homeostasis. It is going to be secreted in
response to low blood calcium levels and triggers osteoclast activity to break down bone and
release calcium into the blood. It is inhibited by negative feedback loop with rising levels of
calcium. The target organs of the parathyroid hormone include the skeleton, the kidneys,
and the intestines. Parathyroid hormone is going to stimulate osteoclast to digest bone matrix
and release calcium into the blood. It also works by enhancing reabsorption of calcium and
secretion of phosphate by the kidneys. Lastly, parathyroid hormones are able to promote
activation of vitamin D by the kidneys. Vitamin D leads to an increased absorption of calcium
by our intestinal mucosa.