tion dedicated to the best use of toxicity data for risk assessment. TERA’s mission is to protect public health by developing and communicating risk-assessment values, by offering consulting services to government and industry, improving risk methods through research, and educating the public on risk assessment issues.13

tetraiodothyronine:

see thyroxine.

thyroglobulin:

a thyroid protein that serves as the substrate for production of thyroxine and triiodothyronine and as the storage form of thyroid hormones.

thyroid:

a butterfly-shaped gland in the front of the neck. It is composed of spherical follicles that are the functional units of the gland.

thyroid follicle:

the functional unit of the thyroid gland, composed of a single layer of thyroid cells surrounding a lumen that contains thyroglobulin, the storage form of thyroxine and triiodothyronine.

thyroid peroxidase:

an enzyme that catalyzes iodide organification into thyroglobulin and then promotes thyroid hormone synthesis.

thyrotropin:

a glycoprotein hormone that stimulates growth and function of the thyroid gland. Also known as thyroid-stimulating hormone.4

thyrotropin-releasing hormone:

a hormone that is released from the hypothalamus and stimulates synthesis and secretion of thyroid-stimulating hormone (TSH).14

thyroxine:

a biologically inactive prohormone containing four iodine atoms that is activated to triiodothyronine by deiodinase. Also known as tetraiodothyronine.

thyroxine-binding globulin:

the primary serum protein that binds thyroid hormones in humans.

TPO:

see thyroid peroxidase.

TRC Companies, Inc.:

a for-profit consulting organization specializing in energy, environment, infrastructure, and infrastructure security projects.15

TRH:

see thyrotropin-releasing hormone.

triiodothyronine:

thyroid hormone containing three iodine atoms. About 80% of the triiodothyronine produced in the body each day is formed outside the thyroid gland by removal of one iodine atom from thyroxine. Triiodothyronine acts in different organs by binding to nuclear thyroid hormone receptors and stimulates or inhibits gene expression.

TSH:

thyroid-stimulating hormone. See thyrotropin.

tyrosine:

an amino acid required for the production of thyroid hormones.


UF:

uncertainty factor. Factors—typically 1, 3, or 10—used to derive an RfD from experimental data. The factors are intended to account for the variation in sensitivity among the members of the human population



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