About the Parathyroid Gland
What is the parathyroid gland?
The body has four parathyroid glands that are located just behind the thyroid gland (which is the center of the neck at the front). They have nothing to do with the function of the thyroid. (PARA is derived from a Greek word meaning beside, alongside of, by.). Very simply, these glands act as a type of thermostat or regulator that controls the blood level of calcium. It is essential to keep the blood level of calcium under tight control because calcium is needed inside just about every cell in the body in order to keep that cell functioning properly. When the blood level of calcium is too high or too low bad things can happen, even to the point of being life-threatening. Fortunately for most people, most of the time these parathyroid glands do their job very well.
How does the parathyroid gland work?
Attached to the cells of these parathyroid glands is a newly discovered molecule called the Calcium Sensing Receptor (CaSR). This CaSR responds to very small changes in the blood level of calcium to turn the parathyroid glands on and off when needed. The CaSR is working as the thermostat. If the body is not getting enough calcium from the diet, for example, the CaSR senses a need to get calcium from somewhere. The immediate response is for the parathyroid glands to make and secrete more of their active hormone – parathyroid hormone (PTH). This sets off a chain of events that get more calcium into the bloodstream. First, PTH goes to the calcium bank – namely your bones where 98% of the body’s store of calcium is warehoused. This is good for the blood calcium and for the cells that need calcium but not good for the bones themselves. The second line of defense against a need for more calcium is the kidneys. Here PTH does two things. First, they limit the kidneys from excreting too much calcium thereby keeping the blood levels up. Next they work on the kidney to produce another hormone called calcitriol or “active vitamin D”. hide
Actually it does many things, but the important one as far as the parathyroid glands and blood calcium are concerned is to help the gut absorb just as much calcium as possible.
The end result is that a limited absorption of calcium from the gut triggers a cascade, in which the parathyroid glands get turned on and produce more PTH, which takes needed calcium from the skeleton and limits excretion of calcium in the urine. PTH also activates the vitamin D system to help the gut absorb as much calcium as possible. Once the levels of calcium have been brought back to normal the system slows down and waits for the next call. Interestingly, and perhaps surprising to most, this chain of events happens without us knowing about or feeling anything wrong. Even the changes in blood calcium that set the whole system in motion are too small to be measured most of the time. The need to keep the blood calcium constant is so great that, when everything is working properly, even the minutest change triggers a response from the parathyroid glands. Yes, vitamin D is actually a hormone not a vitamin. The vitamin D you get from your multi-vitamins, your diet, or that is made by the action of sunlight on your skin is not very active at all. First, it has to go to the liver where it is turned into calcediol, which is more active than vitamin D but still not good enough. This calcediol is then carried in the blood to the kidneys where it is converted to calcitriol. This change from calcediol to calcitriol is controlled by PTH. hide
The end result is that a limited absorption of calcium from the gut triggers a cascade, in which the parathyroid glands get turned on and produce more PTH, which takes needed calcium from the skeleton and limits excretion of calcium in the urine. PTH also activates the vitamin D system to help the gut absorb as much calcium as possible. Once the levels of calcium have been brought back to normal the system slows down and waits for the next call. Interestingly, and perhaps surprising to most, this chain of events happens without us knowing about or feeling anything wrong. Even the changes in blood calcium that set the whole system in motion are too small to be measured most of the time. The need to keep the blood calcium constant is so great that, when everything is working properly, even the minutest change triggers a response from the parathyroid glands. Yes, vitamin D is actually a hormone not a vitamin. The vitamin D you get from your multi-vitamins, your diet, or that is made by the action of sunlight on your skin is not very active at all. First, it has to go to the liver where it is turned into calcediol, which is more active than vitamin D but still not good enough. This calcediol is then carried in the blood to the kidneys where it is converted to calcitriol. This change from calcediol to calcitriol is controlled by PTH. hide
Most of the time you won’t notice anything wrong unless your doctor happens to order a blood calcium test and finds that the level is too high (not uncommon) or too low (quite uncommon). Slightly high blood calcium caused by over-active parathyroid glands can be present for many years without your being aware of it. That does not mean that it might not be doing you any harm. There can be gradual weakening of your bones causing you to be at increased risk for having a fracture. There might also be an increased loss of calcium through the kidneys, increasing your chances of having a kidney stone. In fact, everyone with a fracture that isn’t the result of major trauma and everyone who has a kidney stone should have blood calcium and parathyroid hormone measured. There are even more subtle changes that might be linked to over-active parathyroids. These include an increased risk of high blood diabetes, and very subtle changes in your thinking capacity. These are all very common, even in people with normal parathyroid glands, so the link between the parathyoids and these conditions in any individual patient is not always very clear. Only occasionally are these conditions made better by correcting the abnormal parathyroids. hide
Click to Print This PageTags:
SITEMAP
ENDOCRINE CONDITIONS
RESOURCES
