Thyroid Terms and Definitions

Thyroid Terms and Definitions

by Rashmi Gulati, MD
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Anaplastic Cancer—Also called undifferentiated thyroid cancer, anaplastic thyroid cancer is relatively rare. Unlike other types of thyroid cancer, the symptoms of anaplastic thyroid cancer are usually noticeable right away. Most patients initially complain of difficulty breathing, either shortness of breath or noisy breathing, as well as changes in their voice, usually hoarseness. These changes are the result of the rapidly growing cancer pressing on the windpipe and impinging on the nerves that control the voice. Additionally, most patients notice a large, rapidly growing mass at the front of the neck.

Follicular Cancer—A form of thyroid cancer comprising approximately 25% of all diagnosed thyroid cancers, follicular cancer is usually more aggressive than the more common papillary type. Similar to papillary cancer, however, follicular thyroid cancer is most often discovered as a painless lump in the thyroid, usually after the age of 40, and more often in women than in men.

Graves' disease—A type of autoimmune disorder that causes hyperthyroidism, or overactivity of the thyroid gland, sometimes referred to as toxic diffuse goiter. The thyroid gland helps govern the body's metabolic rate, the rate at which it uses energy. When the thyroid is excessively active, it synthesizes more thyroid hormones than the body requires. High levels of thyroid hormones can cause side effects such as weight loss, rapid heart rate, anxiety and nervousness. This is a disease that affects approximately 2 percent of all women at some point in their lives. Graves' disease most commonly affects women between the ages of 20 and 40, although it occurs in both genders, infants, children, and the elderly.

Hormones—Chemical signaling molecules secreted by endocrine, exocrine, and paracrine glands, tissues, and specialized nerve cells. Concerned with control of body functions, hormones may act as chemical messengers locally to where they are secreted, or upon nearby organs and tissues, or transported peripherally by the bloodstream to affect target receptors on cells in distant organs and tissues. The major glands of the endocrine system include the thyroid, parathyroid, pituitary, adrenal, pancreas, ovary, and testis. Hormone-secreting cells are also present in tissues found in the kidney, liver, gastrointestinal tract, thymus, pineal gland, and placenta.

Hypothalamus—The main function of the hypothalamus is to maintain the endocrine system in a dynamic homeostasis. This state is perhaps more accurately referred to as allostasis, the ongoing process of achieving stability, or homeostasis, through physiological or behavioral change. Factors such as blood pressure, body temperature, fluid and electrolyte balance, and body weight are held within a narrow window of precise values, representing the body's set-point. Although this set-point can migrate over time, from day to day it is remarkably fixed. The hypothalamus also generates behaviors involved in eating, drinking, general arousal, aggression, embarrassment, escape from danger, pleasure and mating.

Medullary Cancer—It is distinctly different from the more common papillary and follicular types of thyroid cancers. In terms of cellular origin, medullary cancer does not arise from the thyroid cells themselves, but rather from the specialized parafollicular cells (also called C-cells) interspersed between the thyroid cells. These cells, which are found located mostly in the upper and middle areas of the thyroid, produce a hormone called calcitonin, levels of which can serve as a marker for medullary thyroid cancer.

Nutraceuticals—Over-the-counter thyroid nutritional supplements, generally defined as any health-enhancing product derived from nature, including plants. Nutraceuticals are natural health products usually packaged in dosage form.

Papillary Cancer—The most common type of thyroid cancer, and the form considered to be most treatable. Most people with papillary thyroid cancer can be completely cured with surgery. There are more than 10,000 new cases of papillary thyroid cancer diagnosed in the United States every year. In fact, papillary cancer comprises at least 70% of all diagnosed thyroid cancers. Most people develop papillary thyroid cancer before age 40, and it is much more common in women than in men. The majority of people with papillary thyroid cancers do not know they have the disease until physical exam by their health care provider reveals a painless thyroid lump.

Pituitary Gland—The pituitary gland is sometimes referred to as the "master" gland of the endocrine system, because it produces hormones that act directly upon a set of other sentinel endocrine glands. However, because the pituitary acts at the express bidding of the hypothalamus, it is the hypothalamus that is the master and the pituitary its slave. The pituitary gland is no larger than a pea, and is located at the base of the brain. The gland is attached to the hypothalamus via nerve fibers.

Thyroidectomy—The surgical procedure involving the removal of one or both lobes of the thyroid gland is termed thyroidectomy. Indications for thyroidectomy may include the presence of a significant mass in the thyroid gland, breathing or swallowing difficulties caused by the impingement of a thyroid mass on the esophagus, goiter, cancer of the thyroid gland, and advanced hyperthyroidism. The decision to recommend thyroidectomy is based on the patient's history, results of physical examination, and tests. Tests commonly required to evaluate the need for thyroidectomy include thyroid hormone panels, fine-needle aspiration biopsy, ultrasound, thyroid scan, CT scan, and/or x-rays. The patient will usually be given general anesthesia. The decision to remove one or both lobes may be made during the course of surgery, with microscopic examination for cellular characteristics of tissue biopsied during surgery.

Citation and Further Reading:

McEwen, B., & Wingfield, J. 2003. The concept of allostasis in biology and biomedicine. Horm Behav., 43 (1), 2-15. URL (abstract): http://www.ncbi.nlm.nih.gov/pubmed/12614627 (accessed 04.24.2010).


Date of Publication: 09/05/2005
Article Last Updated: 01/23/2014

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