The thyroid is a butterfly-shaped gland located in the front of the neck just below the Adams apple. The gland wraps around the windpipe (trachea) and has a shape that is similar to a butterfly formed by two wings (lobes) and attached by a middle part (isthmus). The thyroid gland works like a tiny factory that uses iodine (mostly from the diet in foods such as seafood and salt) to produce thyroid hormones. These hormones help to regulate the body's metabolism and effects processes, such as growth and other important functions of the body.
The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), representing 99.9% and 0.1% of thyroid hormones respectively. The hormone with the most biological power is actually T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted to T3 - the active hormone that affects the metabolism of cells throughout our body.
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Thyroid hormone regulation - the chain of command
The thyroid itself is regulated by another gland located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid (via a "feedback" effect of thyroid hormone on the pituitary gland) and by another gland called the hypothalamus.
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The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a signal to the pituitary to release thyroid stimulating hormone (TSH). In turn, TSH sends a signal to the thyroid to release thyroid hormones. If overactivity of any of these three glands occurs, an excessive amount of thyroid hormones can be produced, thereby resulting in hyperthyroidism. Similarly, if underactivity of any of these glands occurs, a deficiency of thyroid hormones can result, causing hypothyroidism.
Hypothalamus - TRH
Pituitary- TSH
Thyroid - T4 and T3
The rate of thyroid hormone production is controlled by the pituitary gland. If there is an insufficient amount of thyroid hormone circulating in the body to allow for normal functioning, the release of TSH is increased by the pituitary in an attempt to stimulate more thyroid hormone production. In contrast, when there is an excessive amount of circulating thyroid hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone.
There is another hormone that is produced by the thyroid called calcitonin. Calcitonin is produced by specific cells in the thyroid gland, and unlike T3 and T4, it is not involved in this regulation of metabolism. Calcitonin is a hormone that contributes to the regulation of calcium and helps to lower calcium levels in the blood. Excess calcium in the blood is referred to as hypercalcemia.
What types of thyroid disease can occur when the function of the thyroid is affected??
If the thyroid itself is under-active, or if the regulators of the thyroid gland are not functioning properly, hypothyroidism can result. There are many causes of hypothyroidism such as the following:
• Hashimoto's thyroiditis (autoimmune thyroiditis)
• Postpartum thyroiditis (inflammation of the thyroid gland after pregnancy)
• Acute thyroiditis
• Silent thyroiditis
• Thyroid hormone resistance
• Medications that affect thyroid function [such as amiodarone (Cordarone)]
If the thyroid is overactive, or if the regulators of the thyroid gland are pushing the thyroid to produce too much hormone, hyperthyroidism can result. Some of the causes of hyperthyroidism are listed below:
• Graves' disease
• Toxic multinodular goiter
• Toxic nodule ("hot" nodule)
• Excessive intake of iodine
• Hashitoxicosis
• Medications (ingesting thyroid hormone)
What signs and symptoms can occur if thyroid function is affected?
If the thyroid is under-active, symptoms of hypothyroidism may occur. The signs and symptoms of hypothyroidism vary widely, depending on the severity of hormone deficiency. Some of the complaints experienced by patient's with hypothyroidism include:
• fatigue
• mental fogginess and forgetfulness
• feeling excessively cold
• constipation
• dry skin
• fluid retention
• non specific aches and stiffness in muscles and joints
• excessive or prolonged menstrual bleeding (menorrhagia)
• depression
Hyperthyroidism is suggested by a number of signs and symptoms. Patients with mild disease usually experience no symptoms. In patients older than 70 years of age, the classical manifestations may also be absent. In general, the symptoms become more obvious as the condition worsens. The symptoms are usually related to an increase in body metabolism. Common symptoms are listed below:
• Excessive sweating
• Heat intolerance
• Increased bowel movements
• Tremor (usually a fine shake)
• Nervousness; agitation
• Rapid heart rate
• Weight loss
• Fatigue
• Decreased concentration
• Irregular and scant menstrual flow
In older patients, irregular heart rhythms and heart failure can occur. In its most severe form, untreated hyperthyroidism may result in "thyroid storm," a condition involving high blood pressure, fever, and heart failure. Mental changes such as confusion and delirium may also occur. In Graves' disease, there may be eye changes and skin changes in addition to the other findings listed above.
Thyroid Disease Symptoms and Risk Factors for Thyroid Disease
Hypothyroidism Symptoms
The symptoms of hypothyroidism -- an underactive thyroid -- tend to mirror the slowing down of physical processes that results from insufficient thyroid hormone. Common symptoms include fatigue, weight gain, constipation, fuzzy thinking, low blood pressure, fluid retention, depression, body pain, slow reflexes, and much more. A more detailed list of symptoms and risks is featured in the Hypothyroidism Risks/Symptoms Checklist. It can also be helpful to identify risks and symptoms using this interactive online test: Quiz: Could You Be Hypothyroid?.
Hyperthyroidism Symptoms
The symptoms of hyperthyroidism tend to reflect the rapid metabolism that results from an oversupply of thyroid hormone. Common symptoms include anxiety, insomnia, rapid weight loss, diarrhea, high heart rate, high blood pressure, eye sensitivity/bulging and vision disturbances, and many other concerns. A lengthier list of symptoms and risks is featured in Graves' Disease and Hyperthyroidism: Risks and Symptoms. To pinpoint symptoms of an overactive thyroid, you may also want to take this online test: Quiz: Could You Be Hyperthyroid?.
Autoimmune Thyroid Disease Symptoms
The two autoimmune diseases that directly affect the thyroid are Hashimoto's disease and Graves' disease. The symptoms of Hashimoto's disease usually parallel the hypothyroidism that is a result of the disease. Occasionally, however, while the thyroid is failing, it can have periods where it sputters into life and even becomes temporarily overactive. This is known as Hashitoxicosis. Symptoms then can be confusing, with cycling over a period of days or weeks between hypothyroidism and hyperthyroidism symptoms. To understand the difference between hypothyroidism and Hashimoto's disease, read: Hashimoto's vs. Hypothyroidism: What's the Difference? Graves' disease symptoms typically mirror hyperthyroidism. For more information, read this review of important things to know about Graves' disease.
Goiter/Nodules Symptoms
Symptoms of goiter -- an enlarged thyroid -- include a swollen, tender or tight feeling in the neck or throat, hoarseness or coughing, and difficulty swallowing or breathing. Sometimes, the goiter is visbible to yourself or others.
Symptoms of nodules depend on what action they are having. Some cause no symptoms, while others may cause difficulty swallowing, a feeling of fullness, pain or pressure in the neck, a hoarse voice, or neck tenderness. Some nodules trigger hyperthyroid-like symptoms such as palpitations, insomnia, weight loss, anxiety, and tremors. Nodules can also trigger hypothyroidism, and symptoms might include weight gain, fatigue, depression. Nodules can sometimes cause cycling back and forth between hyperthyroid and hypothyroid symptoms.
Here is more information on Thyroid Nodules, Lumps and Goiter. Sometimes you can detect goiter or a nodule yourself by performing a Thyroid Neck Check. Here are instructions on how to do a neck check.
Thyroid Cancer Symptoms
Although many patients are asymptomatic at first, possible symptoms of thyroid cancer include a lump in the neck, voice changes, difficulty breathing or swallowing, or lymph node swelling. A detailed listing of symptoms is featured in the article Thyroid Cancer Symptoms.
Thyroiditis Symptoms
Symptoms of thyroiditis typically include pain and tenderness in the thyroid area, neck and throat, difficulty sleeping. Thyroiditis may also trigger traditional hypothyroid or hyperthyroid symptoms. Some additional information on thyroiditis is featured in this article.
Risk Factors for Thyroid Disease
Some of the key risk factors for thyroid disease include...
• Female: Women are at greater risk than men.
• Age - being 50 and above poses the highest risk of thyroid disease, though it can strike at any age.
• A personal or family history of thyroid and/or autoimmune disease increases risk.
• Surgical removal of all or part of the thyroid, or radioactive iodine treatment to the thyroid -- both which typically result in an underactive thyroid.
• Being left-handed, ambidextrous or prematurely gray mean greater risk of autoimmune disease, including thyroid problems
• Being pregnant or within the first year after childbirth
• Current or former smoker
• Recent exposure to iodine via contrast dye or surgical antiseptic
• Iodine or herbal supplements containing iodine, in pill or liquid form
• Living in an iodine-deficient area
• Various medical treatments, including Interferon Beta-1b, Interleukin-4, immunosuppressants, antiretrovirals, monoclonal antibody (Campath-1H), bone marrow transplant, Lithium, amiodarone (Cordarone), and other medications
• Overconsumption of raw goitrogenic foods, i.e., Brussel sprouts, turnips, cauliflower, soy products and others
• Overconsumption of soy foods
• Recent neck trauma, biopsy, injection or surgery
• Radiation exposure, through radiation to neck area, or exposure to nuclear facility or accident, i.e., Chernobyl
• High stress life events
