The thyroid and the parathyroid are not related in terms of what they do. The prefix “para” means next to; since the parathyroid glands were discovered long after the thyroid and their function was not clear at the time, they were named para-thyroid. They do not have the same function or purpose. There are generally four parathyroid glands, which sit behind or just adjacent to the thyroid.
This is the only organ in the body that has four copies, as every other important organ at most has two copies, such as the lungs and the kidneys. The reason for the large number of parathyroid glands is that it performs a very important function; controlling the level of calcium in your blood. In fact, this is the only responsibility of the gland.
What Does the Parathyroid Gland Do?
Parathyroid glands are part of the endocrine system, which is the hormonal system in the body. This means they control other parts of the body with the chemical they produce called hormones. The purpose of the parathyroid glands is to regulate the calcium level in our bodies within a very narrow range so that all cells in the body can function properly. Remember, every cell in the body uses calcium as a part of its daily workings. The glands measure the amount of calcium in the blood every minute of every day, and if the calcium levels decrease the glands will recognize it right away and make parathyroid hormone.
When the calcium in the blood is high enough again, the parathyroids shut down and stop making parathyroid hormone. The parathyroid hormone or PTH goes to other parts of the body mainly the bones and kidneys and instructs them to increase the calcium in the blood.
We, generally, have four glands, and they are normally the size of a grain of rice. However, occasionally, they can be as large as a pea and still be normal. If you have parathyroid disease, you will most likely have three normal parathyroid glands the size of a grain of rice, and one parathyroid tumor that is as big as an olive or a grape. An over-active parathyroid will make too much parathyroid hormone, causing a potentially serious calcium imbalance. The disease, called hyperparathyroidism, is caused by high PTH levels which in turn cause high calcium levels in the blood.
Blood Calcium Levels
The four parathyroid glands have a very rich blood supply, used to monitor the calcium level in the blood 24 hours a day. On the surface of the parathyroid cells, there is a sensor that acts like a thermostat for calcium levels in the blood. This sensor is called the calcium-sensing receptor. As the blood filters through the parathyroid gland, these receptors detect the level of calcium, and react by adjusting the levels as needed, adding or making less parathyroid hormone.
When the calcium level is low, the cells of the parathyroid releases more parathyroid hormone into the blood, where it circulates to act in a number of places to increase the amount of calcium in the blood. When the calcium level is high, the cells of the parathyroid make less parathyroid hormone, allowing calcium levels to decrease.
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Next, learn about parathyroid disorders.