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Thyroid and Parathyroid Glands by plzchuckle ..... Barefooters' Library

Date:   12/16/2013 10:48:06 AM ( 12 y ago)
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By: Jon Barron



In our last newsletter, we began an exploration of the endocrine system by examining the three endocrine glands in the brain: the hypothalamus, the pituitary, and the pineal gland. In this issue, we move down the body to examine the five endocrine glands found in the neck: the thyroid and the four parathyroid glands. The thyroid gland regulates the rate and intensity of the body's chemical/metabolic reactions, and the parathyroid glands regulate the amount of calcium and phosphorus in the blood. As it turns out, malfunctions in these glands are not that uncommon, can produce serious problems such as over excitement of the muscle and nervous systems, bony demineralization, high calcium levels, duodenal ulcers, kidney stones, and behavioral disorders. And if left unchecked, they can kill you. Fortunately, there are things you can do to minimize the chances of these problems occurring in the first place, or relieving them through alternative means if you get them.


With that in mind, let's begin by looking at the thyroid gland.


Thyroid overview


In essence, the thyroid gland is the thermostat of the body. It regulates both the rate and intensity of chemical/metabolic processes. It is one of the largest endocrine glands in the body and specifically controls how quickly the body uses energy, how it makes proteins, and the body's sensitivity to other hormones. The function of the thyroid gland is to take Iodine and convert it into thyroid hormones -- primarily, thyroxine (T4) and triiodothyronine (T3). Normal thyroid cells accumulate and retain iodide far, far more efficiently than do any other cells in the body. Most cells don't absorb Iodine at all, but some, including thyroid cancer cells and breast epithelial cells, can to a limited degree. Thyroid cells combine Iodine and the amino acid tyrosine (as bound to thyroglobulin) to make T3 and T4. (We will cover this process in more detail a little later.) T3 and T4 are then released into the bloodstream and transported throughout the body, where they control metabolism (i.e., the conversion of oxygen and calories to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism.











Anatomically speaking, the thyroid is a butterfly shaped gland (two larger lobes connected by a narrower isthmus) located between the Adam's apple and the clavicle. When viewed from the front of the body, the thyroid totally covers the trachea. Nevertheless, a normal thyroid gland cannot be felt externally. If a doctor can "see" it or "feel" it when touching the neck with his fingers, it's enlarged. Under normal circumstances, it's soft and flat.


Not surprisingly for such an important organ, it is richly serviced by multiple arteries and veins, which makes surgery on the thyroid that much more difficult. In addition, surgeons face further complications since the nerves that service the vocal cords run right next to the arteries that provide blood to the thyroid. Bottom line is that the thyroid is intricately entwined with key nerves and blood vessels. And it's not just surgery on the thyroid that presents problems. Tracheotomies, for example, must be performed either above or below the thyroid gland. It is also the main reason doctors prefer to "kill" the thyroid with radioactive iodine rather than remove it surgically (a procedure we will talk more about later).



At the micro level, the thyroid is primarily comprised of spheres called follicles. The follicles themselves are primarily composed of two types of cells:



  1. On the outside circumference of the follicles are the cuboidal follicular cells. The follicular cells produce two iodine based compounds, thyroxine (tetraiodothyronine, also known as T4) and triiodothyronine (also known as T3). On the inside circumference, or lumen of the follicle, is a brush border composed of hairlike extensions (not visible in the slide below). This allows for the easy deposit and removal of key hormonal components into the follicular lumen (see slide below) as required for production of T3 and T4.

  2. The parafollicular cells (C cells) sit scattered about the outer edge of the follicles on top of the follicular cells and produce calcitonin, a minor regulator of calcium in the body.












Thyroid hormones


When talking about thyroid hormones, we're actually talking about four bio-chemicals:



As we discussed previously, thyroid chemistry is an iodine-based chemistry; iodine must be ingested because it can't be manufactured in the body; it is an element, not a compound. In fact, follicular cells actively trap virtually all iodine/iodide molecules in the body. Any iodine you ingest is trapped exclusively by cells in the thyroid to be used for manufacturing thyroglobulin and, ultimately, T3 and T4. This fact is exploited by endocrinologists when it comes to treating several thyroid disorders. (We will talk more about this later.) If iodine is not present in sufficient amounts, the body will develop a benign goiter (enlargement of the thyroid) over time. It is common in areas where iodine does not naturally occur in food.



In the early 1900's, Western countries began adding iodine to salt to combat this problem. And it worked, in the sense that goiters are now uncommon in the Western world. But using iodized salt presents its own problems. Surprisingly, a number of "older" societies recognized the connection between iodine and goiters. The ancient Greeks, for example, consumed iodine-rich seaweed to successfully combat goiters -- without the problems associated with iodized salt. Sometimes grandma really does know best.




As seen in the slide above, the thyroid stores something called colloid (which is manufactured in the follicular cells) in the center (lumen) of the follicles in large quantities. Although colloid contains some T3 and T4, it is primarily comprised of thyroglobulin, which is converted to T3 and T4 and released into the body when triggered by thyroid stimulating hormone (TSH), released by the pituitary. In fact, a healthy thyroid stores about a three-month supply of thyroglobulin at any given moment in time.


As we touched on in our last newsletter, thyroid-stimulating hormone (TSH) from the anterior pituitary regulates the processes via a negative feedback loop. That is to say, thyroid releasing hormone (TRH) from the hypothalamus stimulates the pituitary to release TSH into the bloodstream, which stimulates thyroid follicular cells to add iodine to the amino-acid (tyrosine) component of thyroglobulin (which, once again, is stored as colloid within the lumen of the thyroid follicles). Once converted, the T3 and T4 hormones are released into the bloodstream. This arrangement essentially works as a reserve system for thyroid hormones, allowing it to release active hormones into the body on an as needed basis. As more thyroid hormones are produced, blood levels of T3 and T4 rise. Ultimately, these hormones make their way through the bloodstream back to the hypothalamus, telling the hypothalamus that enough is enough and to stop releasing TRH, which stops the pituitary from releasing TSH -- shutting down the cycle.












It should be noted that the thyroid hormones are slow acting. Unlike adrenalin, for example, it takes awhile for anything to happen with thyroid hormones.



Thyroid hormone functions



Thyroid hormones regulate the following activities:




Iodine uptake and control


Iodide (I-) ions circulating in the blood are actively taken into follicular cells through capillaries and become trapped in the endoplasmic reticulum inside the follicular cells. Once iodine is present, the follicles begin synthesizing thyroglobulin. Vesicles (small transport membranes) transport some of the Iodide further into the follicles, where it is combined with thyroglobulin to produce the amino acid tyrosine. This combination of thyroglobulin and tyrosine is bound into colloid, which can be transformed into T3 and T4 as needed.




Incidentally, the thyroid's ability to trap iodine can be used clinically.




Thyroid dysfunction


The two main types of thyroid disease fall into hyperthyroidism (Graves' disease), and hypothyroidism (Hashimoto's thyroiditis).


Hyperthyroidism


Hyperthyroidism causes increased heart rate, increased blood pressure, high body temperature and sweating, nervousness, diarrhea, heat intolerance, and weight loss despite high caloric intake. In other words, the metabolic processes are up regulated to dangerous levels. Also, it can lead to severe neurotic behavior. Graves' disease, a specific form of hyperthyroidism, is an autoimmune disorder in which antibodies mimic the effects of TSH but are not constrained by the negative feedback system for turn-off and control; thus, they continue to drive the thyroid to release stimulating T3 and T4 hormones without letup. This disease causes goiter, enlargement of the thyroid, and exophthalmos (bulging eyeballs caused by the build-up of fat behind the eye). Curing the diseases (often involving the destruction or removal of the thyroid followed by the lifelong administration of synthetic hormones) may not cure exophthalmos, which may leave the eyes open to injury. When talking about Graves' disease and bulging eyes, the late actor, Marty Feldman almost immediately comes to mind.








Hypothyroidism




Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. Early symptoms include:



There are two fairly common causes of hypothyroidism. The first is a result of inflammation of the thyroid gland which leaves a large percentage of the cells of the thyroid damaged (or dead) and incapable of producing sufficient hormone. The most common cause of thyroid gland failure, however, is called autoimmune thyroiditis (aka Hashimoto's thyroiditis), a form of thyroid inflammation caused by the patient's own immune system. (Think of it as the flip side of Graves' disease.)


Dr. Lee covers hypothyroidism in What Your Doctor May Not Tell You about Menopause. First, he points out that thyroid problems are far more common in women than in men -- a strong indicator that we're dealing with an estrogen issue. Then he points out that for most women, when they start using progesterone crème, their need for thyroid supplements is greatly reduced -- and often even eliminated. Note: just because it is more common in women, does not mean that men cannot have estrogen problems also -- caused by exposure to chemical estrogens.


If you suffer from hypothyroidism, removing your thyroid or blasting it with radiation or trying to balance it out with synthetic medication are not your only options. There are natural progesterone crèmes (for both men and women), which easily can be found by searching the net. Also, immunomodulators such as cetyl-myristoleate and L-carnosine might make sense in case the problem is associated with an autoimmune disorder. And finally, thyroid extracts such as Standard Process' Thytrophin PMG can be helpful in rebuilding lost thyroid function.



Cretinism


Hypothyroidism during fetal development totally disrupts normal development patterns, leading to dwarfism, mental retardation, and physical deformities. (Now usually called "thyroid dwarfism.")


Thyroid cancer


Cancerous thyroid tumors (nodules) are most often associated with patients who have had their faces irradiated (at one time this was done to treat acne -- really), but these cancers are easily curable by simply removing the cancerous nodules. Other risk factors include:











The parathyroid glands



The four parathyroid ("beside the thyroid") glands are located on both sides of the thyroid but have functions totally unrelated to the thyroid. This physical relationship of the parathyroids to the thyroid is typical of the endocrine system. Last issue we saw that the pituitary, although extremely small, is comprised of two parts -- anterior and posterior -- that have totally unrelated functions, that develop out of entirely different parts of the body despite their close proximity, and that are for all intents and purposes entirely separate glands. When we explore the adrenals, we will see the same disparate relationship between the adrenal cortex and the adrenal medulla. The bottom line is that the only connection the parathyroids have with the thyroid is their physical location.


Specifically, the parathyroid glands are located behind the thyroid, and they are intimately connected to the covering of the thyroid gland. There are two on each side. They are supplied by the same blood vessels that supply the thyroid. Each parathyroid is about the size of a large kernel of rice. They can be extremely difficult for surgeons to locate and identify. And something that can make the job even harder is that the parathyroid glands sometimes "disengage" from the thyroid gland and migrate down into the chest cavity, making them difficult to find and remove.


So what do the parathyroids do? The chief cells (principal cells) produce parathormone (PTH, parathyroid hormone). The oxyphil cells produce…???? In fact, the function of the oxyphil cells is as yet unknown.


Parathormone, PTH, parathyroid hormone


PTH has one simple function. It regulates the levels of calcium and phosphorus in the blood. It accomplishes this by increasing the cells of the bone (osteoclasts), which reabsorb calcium. It also increases urinary re-absorption of calcium by the kidneys. In addition, it causes the kidneys to form calcitrol, a hormone made from vitamin D that increases absorption of calcium from the GI tract.


And finally, it increases excretion of phosphorus by the kidneys (which, in turn increases calcium levels). Calcium and phosphorus always go in opposite directions -- in a defined relationship called the solubility constant. Bottom line: parathormone increases calcium levels.


Note: Calcitonin (from the thyroid gland) participates in the negative feedback system that regulates the parathyroids by forcing calcium back into the bones.


Pathology of parathyroid dysfunction


Hyperparathyroidism refers to increased PTH production, usually because of a benign tumor of one or more of the parathyroid glands (parathyroid adenoma). If PTH is produced in excess, calcium is reabsorbed from the kidneys, bones, and stomach back into the blood. This leads to a condition that many endocrinologists call "Stones, bones, groans, and moans." This terminology refers to the classic set of four symptoms associated with hyperparathyroidism: kidney stones, de-mineralized bones (osteoporosis), groans of pain from intestinal distress (including duodenal ulcers), and the moans of psychosis.


Hyperparathyroidism is almost always caused by parathyroid adenoma. Removing a parathyroid adenoma, a fairly simple surgery, can cause an immediate and drastic return to normal function and the disappearance of all symptoms.


Another form of hyperparathyroidism is called parathyroid hyperpiesia, in which all four parathyroid glands overproduce PTH for no obvious reason. In other words, there is no adenoma causing the problem. Surgeons usually attempt to fix the problem by removing most of the parathyroid glands.


On the other hand, if the surgeon makes a mistake and removes too much (or all) of the parathyroid tissue by accident, you can end up with hypoparathyroidism. Hypoparathyroidism leads to low serum calcium levels and an elevated state of excitement for nerves and muscles, resulting in twitching and over-activity of the muscular and nervous systems. In the extreme, this can lead to convulsions and death. Again, it is caused primarily by inadvertent surgical removal. This is an extremely difficult condition to live with, as it is almost impossible to self regulate. Fortunately, there is one medical alternative that works in some cases…if the surgeon recognizes the error in time.


Removed parathyroid glands can be chopped up and implanted into muscle tissue in other areas of the body (such as the forearm), where sometimes, they will survive and start producing PTH again. If that doesn't work, hypoparathyroid patients require lifelong calcium and vitamin D injections, which are almost impossible to manage accurately.


Conclusion


When it comes to maintaining the health of the thyroid and parathyroid glands, you want to address several key issues.



In our next issue, we'll move on down the body into the pancreas. In our previous newsletters on the digestive system, we explored the pancreas' production of digestive enzymes. But the pancreas has two distinct functions in the body. In addition to producing digestive juices, it also is part of the endocrine system and produces several key hormones, most notably insulin and ghrelin (the appetite hormone). We will explore those hormones in our next newsletter.







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