Primary and Secondary Hyperparathyroidism

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  • 0:01 The Parathyroid and Calcium
  • 2:12 Primary Hyperparathyroidism
  • 6:01 Secondary Hyperparathyroidism
  • 8:39 Lesson Summary
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Lesson Transcript
Instructor: Jennifer Szymanski

Jen has taught biology and related fields to students from Kindergarten to University. She has a Master's Degree in Physiology.

In this lesson, we'll discuss hyperparathyroidism, overactive parathyroid glands, and highlight differences between the primary and secondary forms of the disease.

The Parathyroid and Calcium

Your skeleton does much more than just provide a framework for your muscles and a system of protection for your organs. It also serves as a storage system for calcium, an ion integral to the proper function of every organ system in the body. Normally, the parathyroid glands play a role in calcium homeostasis by causing release of calcium from this storage system into the blood. Hyperparathyroidism - too much parathyroid hormone - causes the body's system of calcium homeostasis to fail.

Let's start by reviewing a little about the parathyroid glands. Not easily seen because they are hidden behind the much larger thyroid gland, the four parathyroid glands make and secrete parathyroid hormone, or PTH, a hormone that regulates calcium and phosphorous levels. PTH increases the level of calcium circulating in the blood.

Let's see how.

A low level of calcium signals receptors in the parathyroid glands to release PTH. PTH encourages the body to retain calcium by acting on bone, which releases calcium ions; the intestine, which reabsorbs calcium into the bloodstream; and the kidneys, which also reabsorb calcium into the bloodstream. The kidneys activate vitamin D and excrete phosphorous into the urine. As the parathyroid glands' receptors sense rising calcium levels, they signal the parathyroid glands to stop releasing PTH.

An appropriate concentration of calcium in the body is vital. We usually think of bones and teeth when we think of calcium. Although this function of calcium is important, this mineral does much more than just support our skeletal system.

First, cell communication would not be possible without calcium. Calcium plays a major role in delivering biochemical messages needed to produce hormones, neurotransmitters, and other types of cell signals. Calcium is necessary for normal blood clotting. And calcium is crucial for proper muscle contraction and relaxation. All types of muscle - cardiac, smooth, and skeletal - require calcium ions to function.

Primary Hyperparathyroidism

Now that we have in mind basic calcium function and regulation, let's compare the two main types of hyperparathyroidism. As we start, remember that 'hyper' means 'to excess.' For example, when we have too much caffeine, we can get hyperactive - jittery and shaky. This root and its meaning will play a part in several of the terms we're going to use.

In primary hyperparathyroidism, there is a problem with the parathyroid glands that causes them to produce too much PTH. In most cases, this is due to either an adenoma, a non-cancerous tumor of the parathyroid gland, or simple hyperplasia, an increase in the number of cells that make up the parathyroid glands. In both, at least one of the parathyroid glands becomes enlarged. Exactly why adenomas and hyperplasia occur in the parathyroid gland is still unknown, but genetics probably plays a role.

If primary hyperparathyroidism is caused by adenoma, the negative feedback system fails; that is, the receptors that normally tell the parathyroid gland to stop making PTH don't work. In cases caused by hyperplasia, the increase in the number of cells leads to an increase in the amount of PTH. The bottom line? Too much PTH is created and released.

Remembering that PTH's job is to encourage the kidneys and intestine to retain calcium and to release it from bone, it makes sense that an increase in PTH should cause high levels of calcium in the blood. Indeed, this is one of the major symptoms of primary hyperparathyroidism: hypercalcemia.

A classic way to remember specific symptoms of primary hyperparathyroidism is to remember the saying 'bones, stones, abdominal moans, and psychic groans.'

The skeletal system especially suffers from over-release of PTH. Osteopenia - literally 'deficient bones' - results when too much calcium is removed from bones and teeth. Patients experience brittle, fractured or broken bones and bone pain.

The other symptoms in the saying come from hypercalcemia.

Kidney stones are created when excess calcium clogs up the delicate nephrons of the kidney, forming crystals of calcium that condense into stones. Hypercalcemia also causes calcium to spill into the urine. Water follows this excess calcium by osmosis and creates an increase in urine volume.

What about the abdominal moans? Remember, PTH not only encourages calcium uptake from the intestine, it also affects the contraction of the smooth muscle of the digestive tract. Excess PTH causes GI symptoms like nausea, vomiting, abdominal pain, and loss of appetite.

Finally, the psychic groans of the saying stem from hypercalcemia's effect on neurotransmitters. This can cause symptoms like depression and memory problems.

Although not mentioned in the saying, don't forget that cardiac and skeletal muscle are affected, too. Slowed heart rate and increased blood pressure are common, as are tremors, muscle pain, and weakness.

Primary hyperparathyroidism is diagnosed by laboratory tests. These indicate high-circulating levels of PTH, hypercalcemia and low blood phosphorous, as well as calcium in the urine. Surgical removal of the parathyroid glands is the only cure for this type of hyperparathyroidism but is only recommended in severe cases. More moderate cases are treated with calcium supplements of 800-1000 mg per day plus appropriate amounts of vitamin D.

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