Parathyroid glands are small glands which are located in the neck behind the thyroid gland. Parathyroid glands control the calcium in our bodies–how much calcium is in our bones, and how much calcium is in our blood. Calcium is probably the most important element in our bodies (we use it to control many functions), so calcium is regulated very carefully. In fact, calcium is the only element in our bodies that has its own control mechanism. The only function of the parathyroid glands is to control the amount of calcium in our bones and blood.
We all have four parathyroid glands which are normally the size of a grain of rice, but can be as big as a pea. Normal parathyroid glands are the color of spicy yellow mustard. The four parathyroids are usually located behind or around the thyroid gland (“para” means “around”, thus the “para-thyroid” glands are glands that are found around the thyroid gland in your neck). Many people confuse thyroid and parathyroid when they first hear of the parathyroid glands. They have confusing names, and they are located next to each other in the neck, but otherwise the parathyroid glands have a completely separate function from the thyroid gland. Other than being neighbors, the thyroid and parathyroid glands have nothing to do with each other.
Since calcium is so important to our overall health and how we feel, we were all given four parathyroid glands, all doing the same important job—controlling all the calcium in our bodies. We have two parathyroid glands in the left side of our neck and two in the right side. About 1 in 800 people will develop a problem with a parathyroid gland during their lifetime, with the peak incidence between 40 and 70 years of age when about 1 in 400 people will develop an over-active parathyroid gland, usually due to the development of a tumor on one of the glands. When parathyroid glands are behaving well, we have normal blood and bone calcium. When they are not, a number of health problems can occur.
For more information on this topic: http://www.parathyroid.com/parathyroid.htm