Glossary of Terms - t

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Terms

%T3 Uptake: A measurement of the unsaturated thyroxine binding sites of the serum thyroxine binding proteins.
T-uptake: A measurement of the total binding capacity of the thyroxine binding proteins for thyroid hormones.
T3 Thyrotoxicosis: A condition of hyperthyroidism where FT3, but not FT4, is elevated.
Testosterone: A male sex hormone produced mostly by the testicles with a small amount produced by the adrenal glands. Testosterone stimulates a man's sexual activity and growth of other sex organs, including the prostate.
Theophylline: A drug used as a relaxant of bronchial smooth muscle. Toxic levels can cause increased heartbeats, nausea, and seizures. A blood test is available to monitor levels of the drug.
Thyroglobulin (Tg): A protein found in thyroid follicular cells that catalyzes the production of T3 and T4 from MIT and DIT.
Thyroglobulin antibodies (TgAb): Autoantibodies produced by the body against its own thyroglobulin proteins. TgAb attacks the thyroid and disrupts thyroid function.
Thyroid: A butterfly-shaped gland located at the base of the throat that controls metabolism through the secretion of T4 and T3 hormones.
Thyroid cancer: A rare thyroid disease characterized by uncontrolled tissue proliferation in the thyroid.
Thyroid Hormone Binding Ratio (THBR): Recommended nomenclature for T3 Uptake test. A ratio of the solid matrix uptake and the serum uptake.
Thyroid nodules: Masses (usually benign) that can form in the thyroid gland and may produce excessive thyroid hormone.
Thyroid peroxidase (TPO): A protein found in thyroid follicle cells that catalyzes the iodination of T4 and T3 in thyroid hormone biosynthesis.
Thyroid peroxidase antibodies (TPOAb): Autoantibodies produced by the body against its own thyroid peroxidase enzymes. TPOAb attacks the thyroid and disrupts thyroid function.
Thyroid stimulating hormone (TSH): A hormone secreted from the anterior pituitary, that stimulates the thyroid to produce thyroid hormones T4 and T3. Elevated levels of thyroid hormones suppress TSH production by a classical feedback inhibition mechanism.
Thyrotropin releasing hormone (TRH): A tripeptide hormone produced by the hypothalamus which stimulates the anterior pituitary to produce TSH.
Thyroxine (T4): The primary hormone produced by the thyroid. Thyroxin circulates throughout the body primarily bound to carrier proteins. Free T4 is converted to triiodothyronine (T3) in peripheral tissues.
Thyroxine binding globulin (TBG): The major thyroid hormone transport protein in human serum.
Thyroxine binding proteins (TBP): Three serum proteins with binding affinities for T4 and T3; thyroxine binding globulin (TBG), prealbumin, and albumin.
Tissue: A group of cells organized to perform a specialized function.
Titer: The quantity of a substance or its maximal dilution that produces a measurable reaction with another specific substance. Antibody levels (titers) are measured to determine whether they are falling or rising.
Toxic Nodular Goiter: Caused by autonomous production of thyroid hormone by solitary or multiple thyroid nodules.
Toxicology: The science that deals with the study of poisons and their effects in the body, including methods of detection and treatment.
Tricyclic antidepressants: Widely used drugs for the treatment of depression; drug overdose may cause severe toxic effects. The dexamethasone suppression test may aid in the selection of patients who might respond well to antidepressant treatment. Blood and urine tests may be used to determine levels of these drugs in the body.
Triglyceride: A major food fat and blood lipid (fatty substance) produced by the liver from fatty acids. Excess triglycerides are stored in adipose tissue and are used to provide energy. Elevated blood levels of triglycerides and of cholesterol may be associated with an increased risk for atherosclerosis and related disorders, such as coronary artery disease, heart attack, and hypertension.
Triiodothyronine (T3): A thyroid hormone primarily converted from T4, though some excretion occurs from the thyroid directly. T3 is the metabolically active hormone.
Tumor: An abnormal growth of cells resulting from uncontrolled cell growth.
Turner syndrome: A chromosomal abnormality in women in whom only one X chromosome is present instead of the normal two. The condition is characterized by growth abnormalities such as dwarfism and underdeveloped reproductive organs. Learning problems and mild mental retardation may be present. A smear of scrapings from inside the mouth may show evidence of this condition. Culture and chromosomal analysis of fetal cells from amniotic fluid can forecast this syndrome.
Type 1 diabetes: A condition characterized by abrupt onset of symptoms, insulinopenia, dependence on exogenous insulin to sustain life and a tendency to develop ketoacidosis.
Type 2 diabetes: A disorder usually characterized by a gradual onset with minimal or no symptoms of metabolic disturbance, exogenous insulin is not required to prevent ketonuria and ketoacidosis; dietary control and exercise with or without oral diabetes medications is usually effective.