Normal Parathyroid Gland Function: Learn how parathyroid glands make parathyroid hormone and control calcium in the blood and bones.

The sole purpose of the parathyroid glands is to control calcium within the blood in a very tight range between 8.8 and 10.2.  In doing so, parathyroids also control how much calcium is in the bones, and therefore, how strong and dense the bones are. Although the parathyroid glands are located next to (and sometimes inside) the thyroid gland, they have no related function. The thyroid gland regulates the body’s metabolism and has no effect on calcium levels while parathyroid glands regulate calcium levels and have no effect on metabolism. Calcium is the element that allows the normal conduction of electrical currents along nerves--its how our nervous system works and how one nerve 'talks' to the next. Our entire brain works by fluxes of calcium into and out of the nerve cells. Calcium is also the primary element which causes muscles to contract. 

Knowing these two major functions of calcium helps explain why people can get a tingling sensation in their fingers or cramps in the muscles of their hands when calcium levels drop below normal. A sudden drop in the calcium level (like after a successful parathyroid operation where the patient doesn't take their calcium pills for the first few days after the surgery) can cause patients to feel "foggy", "weird" or "confused like my brain isn't working correctly". The brain DEMANDS a normal steady-state calcium level, so any change in the amount of calcium can cause the brain to feel un-loved and the patient to feel bad.  Likewise, too much parathyroid hormone causes too high a calcium level--and this can make a person feel run down, cause them to sleep poorly, make them more irritable than usual, and even cause a decrease in memory. In fact, the most common symptoms for patients with parathyroid disease are related to the brain, and include depression and lack of energy! After removal of a bad parathyroid gland, most people will feel dramatically better. Some say its like "someone turned the lights on". Most people don't feel good when their calcium level is above 10, and the vast majority of people will feel pretty darn tired and run-down when their calcium level is above 10.5.  Go to the page on Symptoms of Hyperparathyroidism to lean more about symptoms of high calcium.

NORMAL PARATHYROID ACTIVITY

Although the four parathyroid glands are quite small, they have a very rich blood supply. This suits them well since they are required to monitor the calcium level in the blood 24 hours a day. As the blood filters through the parathyroid glands, they detect the amount of calcium present in the blood and react by making more or less parathyroid hormone (PTH). When the calcium level in the blood is too low, the cells of the parathyroids sense it and make more parathyroid hormone. Once the parathyroid hormone is released into the blood, it circulates to act in a number of places to increase the amount of calcium in the blood (like removing calcium from bones). When the calcium level in the blood is too high, the cells of the parathyroids make less parathyroid hormone (or stop making it altogether), thereby allowing calcium levels to decrease. This feed-back mechanism runs constantly, thereby maintaining calcium (and parathyroid hormone) in a very narrow "normal" range. In a normal person with normal parathyroid glands, their parathyroid glands will turn on and off dozens of times per day...in an attempt to keep the calcium level in the normal range so our brain and muscles function properly. Those of us with normal parathyroid function will have calcium levels that are constant... with almost zero variability. For instance, if your calcium level is 9.6 this week and you have normal parathyroid glands, your calcium will be between 9.4 and 9.8 every time you measure it for most of your life.  Contrast this with somebody that has a bad parathyroid gland. The bad parathyroid gland has lost it's regulatory system and these patients have calcium levels that bounce around from high to low, never the same number twice: up - down, up - down, up, up, down, up, up, down. The control system is lost in parathyroid tumors. This is hyperparathyroidism.

HOW DOES PARATHYROID HORMONE INCREASE BLOOD CALCIUM ?

Like all endocrine glands, parathyroids make a hormone (a small protein capable of causing distant cells in the body to react in a specific manner). Parathyroid hormone (PTH) has a very powerful influence on the cells of the bones which causes them to release their calcium into the bloodstream. Calcium is the main structural component of bones which give them their rigidity--but remember from our first page, the principle purpose of the bones is to provide a storage system for calcium--so our brain will never be without calcium. Under the presence of parathyroid hormone, bones will give up their calcium in an attempt to increase the blood level of calcium. Under normal conditions, this process is very highly tuned and the amount of calcium in our bones remains at a normal high level. Under the presence of too much parathyroid hormone, however, the bones will continue to release their calcium into the blood at a rate which is too high resulting in bones which have too little calcium. This condition is called osteopenia and osteoporosis and is illustrated in the bone segment on the top which has larger "pores" and less bone mass. When bones are exposed to high levels of parathyroid hormone for several years they become brittle and much more prone to fractures. Another way in which the parathyroid hormone acts to increase blood levels of calcium is through its influence on the intestines. Under the presence of parathyroid hormone the lining of the intestine becomes more efficient at absorbing calcium normally found in our diet.

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