Video Transcript
What hormone is produced by the thyroid gland to decrease calcium levels in the
blood?
This question asks us about the thyroid gland specifically, so let’s discuss what
role the thyroid gland plays in the human body.
The thyroid gland is an organ in the endocrine system. The endocrine system is a series of glands that produce and secrete hormones that the
body uses for a wide range of functions. These include the regulation of body metabolism, growth of body tissues,
reproduction, and blood pressure.
The endocrine glands are able to influence so many different processes because they
release hormones directly into the bloodstream. The hormones are then carried to their target cells, where they bring about a
response.
The master gland in the endocrine system is called the pituitary gland. It is called the master gland because it stimulates other organs, such as the thyroid
gland, adrenal glands, ovaries, and testes, to produce their respective
hormones. As you have just seen, one of the organs that the pituitary gland influences is the
thyroid gland. The thyroid gland is a butterfly-shaped gland, found in the base of the neck.
The pituitary gland releases thyroid-stimulating hormone, or TSH, which enters the
blood and is carried all around the body. When it reaches the thyroid gland, it attaches to receptors on the surface of its
secretory cells. This stimulates the thyroid gland to release the thyroid hormones thyroxine and
triiodothyronine. These hormones regulate many different processes, such as the ones mentioned earlier:
metabolism, growth, development, and blood pressure.
The thyroid gland also releases another hormone, called calcitonin. The secretion of this is not controlled by thyroid-stimulating hormone; instead it is
controlled by calcium ions in the blood. When blood calcium levels rise, calcitonin is released, bringing the levels back down
to normal, an example of negative feedback. This occurs through osteoclast inhibition. Osteoclasts are cells that degrade bones and release their stored calcium into the
bloodstream. Osteo- means bone and “clast” refers to a cell that destroys. By inhibiting this activity, blood calcium levels are decreased. Calcitonin will also increase the excretion of calcium in urine.
Now that we have reviewed some of the main facts about the endocrine system and the
three main hormones of the thyroid gland, let’s take another look at our
question. We are asked what hormone is produced by the thyroid gland to decrease calcium levels
in the blood. We now know that the answer is calcitonin.
