What is the Difference Between Thyroid and Parathyroid Glands?
When evaluating patients with thyroid and parathyroid gland problems over the years, I have heard the same comments from them over and over again. At the top of the list is “I did not even know I had parathyroid glands”, followed by “what is the difference between my thyroid and parathyroid glands, do they do the same things?”.
This is understandable since everybody has heard of a thyroid gland, but most people don’t even know they have a parathyroid gland (or 4 of them). The thyroid and parathyroid glands, while sharing similar names (more on this later), have no functional relationship at all – they do completely different but equally important things to keep your body working properly. Let’s take a look at the differences between thyroid and parathyroid glands.
What is the Difference Between Thyroid and Parathyroid Glands?
Difference #1 Between Thyroid and Parathyroid Glands: They have completely different functions
Our Thyroid Gland’s Job
We all have one thyroid gland, located in the front of the neck. While this gland is relatively small (about the size of a walnut in most of us—located on both sides of the trachea), it has a very important job, which is to control our body’s metabolism – its production of the energy the drive all the processes and functions that keep us going. Your thyroid gland uses iodine from the foods you eat and combines it with the amino acid tyrosine to produces two hormones, triiodothyronine (T3 – 3 iodine atoms) and thyroxine (T4 - 4 iodine atoms). While your thyroid gland produces significantly more T4 than T3, T4 is converted to T3 in other tissues in your body (such as the liver), with T3 being 3-4 times more potent than T4.
Your brain, specifically the pituitary, gland controls how much thyroid hormone your thyroid secretes with another hormone – thyroid stimulating hormone (TSH). When your body needs more thyroid hormone, the pituitary secretes more TSH, which in turn tells your thyroid to make and secrete more T4 and T3 (figure1). Essentially every cell in our bodies relies on thyroid hormone to control its metabolism – the conversion of oxygen and calories into energy.
Our Parathyroid Gland’s Job
Most of us have four parathyroid glands (in rare cases we can have more than four). This is a redundant system, with all four glands producing the same hormone – parathyroid hormone (PTH). PTH has one job, which is to regulate the levels of calcium in our bloodstream. While this may not sound like an important job, calcium is intimately involved in many crucial biological functions. For example, the process of nerve conduction involves a tightly regulated flow of calcium (and other) ions in and out of the nerve cells throughout our body. Additionally, muscle contraction relies on a similar process of regulated flow of calcium (and other) ions in and out of our muscle cells. Calcium is therefore important for the proper function of our musculoskeletal system, our cardiovascular system, and our nervous systems.
It is normal for calcium levels to fluctuate to some degree in our bloodstream, depending upon how much our body is using and how much we have taken in through our diet, etc. This is no problem within a certain range of concentration. However, when the concentration of calcium drops below a set point, the cells in our parathyroid glands sense this and secrete PTH in response. This hormone then does three main things to increase the concentration of calcium in our bloodstreams. First, PTH activates cells in your bones (called osteoclasts), which then break down bone mineral releasing calcium from the bones into the blood. PTH also acts within the kidneys so less calcium is filtered into our urine and stays instead within our bloodstream. Finally, PTH converts vitamin D from its less active form (25-hydroxy vitamin D) to its more active form (1,25 dihydroxy vitamin D). This activated vitamin D facilitates absorption of calcium in your intestines. Once the calcium concentration is back up where we need it, our parathyroid glands once again sense this and PTH secretion slows down.
There you have it – a crash course in thyroid and parathyroid physiology and how they are different. Learn more about parathyroid function here.
Difference #2 Between Thyroid and Parathyroid Glands: Their location within the neck
Normal Locations for the Thyroid and Parathyroid Glands
The thyroid and parathyroid glands live fairly close to each other in the low part of our necks. The thyroid gland is draped over the windpipe (trachea), with a left and right lobe connected in the center by a bridge of thyroid tissue called the isthmus. It is situated about half an inch below our “Adams Apple” (thyroid cartilage), is butterfly shaped, and in most people is about the size of a walnut. The thyroid is held in this position by a strong band of connective tissue between itself and the trachea, as well as the blood vessels feeding into and out of it.
The parathyroid glands typically are located in close proximity to the thyroid gland, and are much smaller in size. A normal parathyroid gland ranges in size between a grain of rice and a kernel of corn. While these glands are often described as being “behind” the thyroid gland, this is a bit simplistic. As mentioned above, most people have four parathyroid glands – two embryologic upper glands and two embryologic lower glands. The upper glands are located further back in the neck, so it is accurate to say in most cases that these glands are “behind” the thyroid gland - usually the upper part of each lobe (the upper pole). The lower glands have more “normal” variability in where they are located, with common locations being behind, on the side, or just below the lower part of each lobe (lower pole). (figure 2)
Abnormal Locations for Thyroid and Parathyroid Glands
The above describes the homes of our thyroid and parathyroid glands in MOST people. However, both the thyroid and parathyroid glands can end up living in some less common locations. This has to do with what happens when early in our development (embryology). Our thyroid gland begins its development in the same tissue that becomes our tongue. As we develop, the thyroid moves down from the tongue through the floor of the mouth until it takes up its normal home as described above.
Sometimes, though, things do not proceed as planned. A relatively common abnormality is for some thyroid tissue to be left behind during the descent from the tongue. A rare occurrence is for the thyroid to never leave the mouth, with some people having their thyroid glands located in the back of their tongues. Also rare is the thyroid gland migrating lower than it is supposed to and ending up entirely in the chest. Functionally, these errors during development are of no consequence. It only becomes important if thyroid surgery becomes necessary.
The parathyroid glands undergo a similar migration during embryology, with the tissue that becomes these glands beginning in what becomes our head and migrating south into their normal locations in the neck as described above. As with the thyroid, errors can occur during this migration with parathyroid glands ending up located well above the thyroid gland near the angle of the jaw, well below the thyroid gland in the chest near the heart, hidden amongst the large vessels in the neck (carotid artery and jugular vein), or hidden inside the thyroid gland itself (figure 3). When having surgery of the thyroid and parathyroid glands it is very important to have a surgeon with intimate knowledge and understanding of the embryology and both normal and ectopic anatomy to ensure a successful outcome.
Learn more about our expert thyroid and parathyroid surgeons here.
Difference #3 Between Thyroid and Parathyroid Glands: They develop different problems and diseases
There are two main types of problems that can occur with your thyroid gland – structural problems and functional problems. Structural problems include the development of one or more nodules within the thyroid or a generalized enlargement of the thyroid. Nodules in the thyroid are common and generally are nothing to worry about, but their presence may lead to thyroid surgery if there is concern for thyroid cancer or if they become large enough that they cause problems due to compression of the windpipe or the esophagus.
Learn more about thyroid nodules and thyroid cancer and thyroid surgery here.
Functional problems with the thyroid can be due to the production of too much or too little thyroid hormone. The production of too much thyroid hormone can be due to one or more thyroid nodules not following the rules and making too much hormone (toxic nodule or toxic multinodular goiter), Graves disease where antibodies attach to thyroid cells and activate the thyroid gland continuously, as well as some medications (amiodarone). Hyperthyroidism can cause a slew of symptoms and health problems so treating it is important. This can involve medical therapy (most cases of Graves disease) or surgical therapy (toxic nodule or toxic multinodular goiter).
Making too little thyroid hormone is cause in most cases by an autoimmune condition. About 20% of the population make antibodies to their own thyroid glands and slowly destroy it. As more and more thyroid cells are killed by these antibodies, not enough thyroid hormone can be produced to maintain the body’s metabolism. This is treated medically with thyroid hormone supplementation – T4 synthesized in the lab and given in the form of a pill.
Parathyroid glands can cause problems when one or more of them become hyperfunctioning – they secrete PTH constantly rather than only when you calcium levels are low and your body needs it. This is called primary hyperparathyroidism. It occurs more commonly in women than men (3 to 1) and is most commonly seen in people in their 60’s. In most cases this is the result of a benign tumor (adenoma) developing in one of the glands. The tumor cells do not follow the rules, so to speak, so rather than raising low calcium concentrations to normal, the constant secretion of PTH raises calcium levels above normal. Over time, primary hyperparathyroidism has serious health consequences including the development of kidney failure, increased risk of heart attacks and stroke, and osteoporosis. Hyperparathyroidism can also cause a number of debilitating symptoms. Because of this, hyperparathyroidism should always be treated when diagnosed. This involves surgical removal of the gland with the tumor in it. There is NO medical treatment for primary hyperparathyroidism. For more information about hyperparathyroidism click here: https://www.parathyroid.com
Difference #4 Between Thyroid and Parathyroid Glands: One can develop cancer and one cannot
Thyroid Cancer is Common
Cancer of the thyroid gland is relatively common, with around 50,000 new cases diagnosed in this country every year. There are several types of thyroid cancer, with the most common by far being papillary thyroid cancer. Other types include follicular, medullary, and poorly differentiated or anaplastic thyroid cancer. Fortunately, the most commonly occurring type (papillary) is very successfully treated in most cases. The less common types are more aggressive and harder to treat successfully, with anaplastic thyroid cancer being one of the most aggressive cancers we can have.
Parathyroid Cancer Is Extremely Rare
As mentioned previously, hyperparathyroidism is caused in the majority of cases by a tumor growing in one of the parathyroid glands. However, these are BENIGN tumors – there is no chance these tumors can invade other tissues or spread to other areas of the body. Parathyroid glands can develop cancer – you will see sections in textbooks describing it – but it is so exquisitely rare that most doctors who take care of parathyroid patients never see it once in their whole careers. Again – the reason hyperparathyroidism needs to be treated is because the overproduction of PTH and the resulting elevated calcium levels cause end organ damage over time, not because there is any concern for cancer.
Difference #5 between Thyroid and Parathyroid Glands: Thyroid and parathyroid surgery is completely different
How the Thyroid Gland Relates to Parathyroid Surgery
Despite being close to each other anatomically, surgery for problems with the thyroid and parathyroid glands is quite different. Surgery for hyperparathyroidism involves finding and removing the hyperfunctioning gland. While the thyroid is not related to the problem of hyperparathyroidism per se, because of the proximity of the thyroid and parathyroid glands to each other, it can become an issue during a parathyroid operation.
For example, it is not unusual to encounter thyroid nodules during a parathyroid operation. These need to be evaluated and if there is any concern for thyroid cancer then they should be biopsied/removed as part of the parathyroid surgery. In other circumstances, the thyroid can be significantly enlarged or friable, making it more difficult to locate the normal and abnormal parathyroid glands. It is very important to have an experienced parathyroid surgeon who is capable of dealing with these thyroid-related issues to ensure a good outcome.
How the Parathyroid Glands Relate to Thyroid Surgery
Surgical removal of the thyroid gland involves freeing it from its attachments in the neck. As mentioned earlier, this includes the connective tissue attachments between the thyroid and the trachea and the blood vessels supplying the gland. This is a delicate business, as there are nearby structures that are important to keep safe, including the parathyroid glands. With the thyroid and parathyroid glands being so close to each other, it can take significant surgical skill to remove the thyroid while preserving the parathyroid glands. Thyroid surgeons also must be able to recognize an unsuspected parathyroid adenoma when they encounter it during a thyroidectomy and be sure to remove it.
Surgery of the thyroid and parathyroid glands is very specialized and requires a great deal of experience for successful outcomes.
Learn more about the surgical diseases of the thyroid and parathyroid glands and the expert surgeons who treat them.