What is the Thyroid?

The thyroid is a small gland, shaped like a butterfly, located in the lower part of your neck. The function of a gland is to secrete hormones. The main hormones released by the thyroid are triiodothyronine, abbreviated as T3, and thyroxine, abbreviated as T4. These thyroid hormones deliver energy to cells of the body.The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck just below the Adam’s apple. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones. The thyroid participates in these processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is an essential component of both T3 and T4. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.
The thyroid is controlled by the hypothalamus and pituitary. The gland gets its name from the Greek word for “shield”, after its shape, a double-lobed structure. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland. Specialists are called Thyroidologists

What Diseases and Conditions Affect the Thyroid?

The most common problems that develop in the thyroid include:• Hypothyroidism — An underactive thyroid.
• Hyperthyroidism — An overactive thyroid.
• Goiter — An enlarged thyroid.
• Thyroid Nodules — Lumps in the thyroid gland.
• Thyroid Cancer — Malignant thyroid nodules or tissue.
• Thyroiditis — Inflammation of the thyroid.

Hypothyroidism

When the thyroid gland is underactive, improperly formed at birth, surgically removed all or in part, or becomes incapable of producing enough thyroid hormone, a person is said to be hypothyroid. One of the most common causes of hypothyroidism is the autoimmune disease called Hashimoto’s disease, in which antibodies gradually target the thyroid and destroy its ability to produce thyroid hormone.
Symptoms of hypothyroidism usually go along with a slowdown in metabolism, and can include fatigue, weight gain, and depression, among others.

Causes of Hypothyroidism

Loss of tissue: Treatment of hyperthyroidism by radioactive destruction of thyroid tissue or surgical removal of thyroid tissue can result in hypothyroidism.
Antithyroid antibodies: These may be present in people who have diabetes, lupus, rheumatoid arthritis, chronic hepatitis, or Sjögren syndrome. These antibodies may cause decreased production of thyroid hormones.
Congenital: Hypothyroidism can be present from birth. This is commonly discovered early with nationwide newborn screening for this disease.
Defects in the production of thyroid hormone: Hashimoto thyroiditis occurs when there are defects in the production of thyroid hormone, resulting in an increased amount of TSH. The increased TSH results in a goiter (enlargement of the thyroid gland itself that can be seen as an obvious swelling in the front of the neck)

Hyperthyroidism

When the thyroid gland becomes overactive and produces too much thyroid hormone, a person is said to be hyperthyroid. The most common cause of hyperthyroidism is the autoimmune condition known as Graves disease, where antibodies target the gland and cause it to speed up hormone production.

Causes of Hyperthyroidism
  • Graves disease: This thyroid condition results from abnormal stimulation of the thyroid gland by a material in the blood termed the long-acting thyroid stimulator (LATS). LATS overstimulates the thyroid causing a goiter. It also causes Graves eye disease, including a “bug-eyed” look and “frightened stare.” This can progress to severe eye pain or eye muscle weakness. It also causes raised, thickened skin over the shins or tops of the feet.
  • Toxic multinodular goiter: This occurs when part of the thyroid gland produces thyroid hormones all by itself, without regard to TSH stimulation. It usually occurs in people with a long-standing goiter—usually in the elderly. Toxic multinodular goiter is different from Graves disease because of the general lack of eye complications and less severe signs of hyperthyroidism.
  • Thyroiditis: This inflammatory disorder of the thyroid gland includes such conditions as de Quervain thyroiditis or Hashimoto thyroiditis. In these conditions, you may have periods of increased thyroid hormone release due to the inflammation, causing a hyperthyroid state. As thyroid failure occurs due to the inflammatory response, hypothyroidism may occur.
  • Pituitary adenoma: This tumor of the pituitary gland causes independent TSH production leading to overstimulation of the thyroid gland.
  • Drug-induced hyperthyroidism: This is most commonly caused by a heart medication called amiodarone. It may be prevented by monitoring this possible side effect and weighing it against the benefits of using the heart medication.

How Does Your Doctor Make The Diagnosis?

The diagnosis of a thyroid abnormality in function or a thyroid mass is made by taking a medical history and a physical examination. Specifically, your doctor will examine your neck and ask you to lift up your chin to make your thyroid gland more prominent. You may be asked to swallow during the examination, which helps to feel the thyroid and any mass in it. Other tests your doctor may order include:• An ultrasound examination of your neck and thyroid
• Blood tests of thyroid function
• A radioactive thyroid scan
• A fine needle aspiration biopsy
• A chest X-ray
• A CT or MRI scan

Sources: Synthroid, About Thyroid

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