Hypothyroidism: Glossary

Here are definitions of medical terms related to hypothyroidism.

Adam’s apple: This part of the cartilage that forms the larynx, or voice box, can be felt at the front of the neck. It is more prominent visually and by touch in men than in women.

Anemia: Any condition characterized by a low red blood cell count. A low red blood cell count decreases the body’s ability to use oxygen, and thus, to work. Anemia is associated with easy fatiguing, even with mild exertion.

Angina (or angina pectoris): A sudden pain that can be felt in the chest, lower jaw, or down the left arm that is due to insufficient blood flow to heart muscle, usually due to narrowing of the coronary arteries, the arteries that supply the heart muscle with blood.

Antibody: A protein made by the body’s immune system to defend the body against a foreign substance like a virus, bacterium or other foreign body, most often a foreign protein. Rarely, the body’s immune system may mistakenly make antibodies against itself. This is an abnormal or autoimmune response.

Antithyroid drug: Any one of several agents used to treat hyperthyroidism that decreases production of thyroid hormone within the thyroid gland.

Autoimmune disorder: An autoimmune disorder is one in which the body’s immune system mistakenly “attacks” its own healthy tissue.

Cholesterol: A fatty substance found naturally in animal cells, including human cells. High levels of cholesterol in the blood are correlated with arteriosclerosis, the condition marked by deposits of fatty materials inside blood vessels leading to their narrowing or obstruction.

Endocrine gland: A gland that releases a chemical messenger, known as a hormone, directly into the bloodstream, that will affect other parts of the body. The thyroid is an endocrine gland.

Endocrinology: The subspecialty within internal medicine devoted to disorders of the endocrine glands. The specialist is called an endocrinologist.

Goiter: An enlarged thyroid gland due to any cause. It is seen as a swelling or fullness in the front of the neck.

Graves’ disease: An autoimmune disorder in which the immune system attacks the cells of the thyroid gland causing hyperthyroidism. Hyperthyroid eye changes and skin changes are sometimes associated with it.

Hashimoto’s thyroiditis: An autoimmune disorder of the thyroid gland in which the body’s immune system attacks the thyroid gland, destroying the cells of the thyroid gland

Hormone: A chemical substance that is produced by an endocrine gland and released into the bloodstream to have its effect on other parts of the body. Also known as a “chemical messenger”. For example, thyroid hormone, released by the thyroid gland speeds up or stimulates certain bodily functions.

Hyperthyroidism: A condition in which too much thyroid hormone is circulating throughout the body, causing excessive stimulation of metabolic activity in body cells.

Hypothyroidism: A condition in which too little thyroid hormone is circulating throughout the body, causing inadequate stimulation of metabolic activity in body cells.

Immune system: The body system (consisting primarily of white blood cells) that enables the body to fight infection and defend itself against foreign invaders.

Infertility: Inability to become pregnant.

Iodine: A chemical element found naturally in seawater and some other sources that is needed to produce thyroid hormone. Iodized table salt has had iodine added to it.

Juvenile diabetes mellitus: Also known as insulin-dependent diabetes, this form of the disease most commonly develops in children and young adults.

Metabolism: The chemical and physical processes in the body that create the substances and generate the energy needed for cells to function, grow normally, and divide. Metabolism is also known as metabolic activity.

Pernicious anemia: A form of anemia, which means less than the normal level of circulating red blood cells. This condition is caused by an inappropriate autoimmune process in which the immune system attacks and damages certain cells lining the stomach. As a result, vitamin B12 is not absorbed properly from food that is consumed. Vitamin B12 is necessary for proper red blood cell production.

Pituitary gland: A relatively small endocrine gland about the size of a pea. This gland is located underneath the brain and releases a number of essential hormones, including thyroid stimulating hormone (TSH).

Placenta: The structure within the pregnant uterus that is the interface between the maternal and fetal bloodstreams. Oxygen, food substances, and other materials pass from the mother’s bloodstream to the fetus’s through the placenta. Many drugs cross the placenta to enter the fetal bloodstream.

Postpartum thyroiditis: Inflammatory condition of the thyroid probably of autoimmune origin. It occurs in 5%-9% of women following childbirth. Although the hypothyroidism associated with it is usually temporary, it can become permanent in up to one third of affected women.

Radioactive iodine: Chemically depicted as 131I, this form of iodine is radioactive, which means it emits intense energy due to chemical reactions in the nucleus. It is often used in the treatment of hyperthyroidism.

Subacute thyroiditis: Inflammatory condition of the thyroid of unclear origin, it often follows an upper respiratory infection. The hyperthyroidism and hypothyroidism associated with it is usually mild and temporary.

Synthetic thyroid hormone: Thyroid hormone (T4) that is artificially manufactured but is structurally identical to that naturally produced in the body.

T3: A term used to describe a form of thyroid hormone in the bloodstream. It has three units of iodine attached to the hormone structure. T3 is biologically active.

T4: A term used to describe a form of thyroid hormone in the bloodstream. This form has four iodine units attached to the hormone structure. Most thyroid hormone in the blood is T4; however, it is not biologically active in the body. Special cells convert T4 into T3.

Thyroid gland: Small, butterfly-shaped organ located in the neck below and in front of the Adam’s apple, which produces thyroid hormone.

Thyroid hormone: Chemical substance produced by the thyroid gland and released into the bloodstream. It interacts with almost all body cells, causing them to increase their metabolic activity. Two forms of thyroid hormone, abbreviated as T3 and T4, are found in blood.

Thyroid-stimulating hormone (TSH): Hormone produced by the pituitary gland that interacts with thyroid cells causing them to produce and release more thyroid hormone into the blood.

Vitamin B12: A chemical substance found almost exclusively in meats that is necessary for certain chemical processes in the body, including the ongoing production of red blood cells.

Vitiligo: An autoimmune skin disorder caused by attack of the immune system on the pigment-producing cells within the skin. The loss of the cells responsible for skin color result in milky white patches on the skin surface.


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