 FOLDER 21.4 Clinical Correlation: Abnormal Thyroid Function aaabbbFIGURE F21.4.1 • Hyperthyroidism. a. A young woman with signs of hyperthyroidism. Note the enlarged mass on the neck and the typical ocular symptoms known as exophthalmos. b. Photomicrograph of a thyroid gland specimen from an individual with Graves’ disease. Due to the increased utilization of colloid, there is a lack of staining at the periphery of the colloid near the apical surface of the follicular cell. Note that the majority of the cells are columnar in shape. (Reprinted with permission from Rubin E, Gorstein F, Rubin R, Schwarting R, Strayer D. Rubin’s Pathology, Clinicopathologic Foundations of Medicine, 4th ed. Baltimore: Lippincott Williams & Wilkins, 2005.)
TABLE 21.7 Hormones of the Thyroid Gland carbohydrate use, protein synthesis and degradation, and fat synthesis and degradation); regulates heat production; influences body and tissue growth and development of the nervous system in the fetus and young childb; increases absorption of carbohydrates from the intestine
Decreases blood calcium levels by inhibiting bone resorption and stimulating absorption of calcium by the bones
Thyroxine (tetraiodothyronine, T4) and aThyroid gland secretes substantially more T4 than T3; however, about 40% of T4 is peripherally converted to T3, which acts more rapidly and is a more potent hormone. bDeficiency of T3 and T4 during development results in fewer and smaller neurons, defective myelination, and mental retardation.
blood into their cytoplasm using ATPase-dependent lishing an intracellular concentration of iodide that is 30 sodium/iodide symporters (NIS). The NIS is the to 40 times greater than that of the serum. Iodide ions 87-kilodalton transmembrane protein that mediates ac-then diffuse rapidly toward the apical cell membrane. tive iodide uptake in the basolateral membrane of the From here iodide ions are transported to the lumen of follicular epithelial cells. These cells are capable of estab-the follicle by the 86 kilodalton iodide/chloride receptor FIGURE 21.16 • Diagram of steps in thyroid hormone synthesis. This diagram 5L depicts two follicular cells: one in the process of thyroglobulin synthesis (on the left with red pathways) and the other in the process of thyroglobulin resorption (on the right with blue pathways). The numbers, which are described more fully in the text, indicate the sequential steps that occur: 1, synthesis and secretion of thyroglobulin; 2, uptake and concentration of iodide from the blood by sodum/iodide symporters (NIS), release of iodide into the colloid via iodide/chloride (pendrin) 6 transporters, and oxidation of iodide to iodine by thyroid peroxidase; 3, iodination of thyroglobulin in the colloid; 4, formation of T3 and T4 hormones in the colloid by oxidative coupling reactions; 5L, resorption pathway); 5TE, resorption of colloid via pathway; and 6, release of T4 and T3 from synthesis resorption the cell into the circulation.
transporter called pendrin located in the apical cell membrane. Iodide is then immediately oxidized to iodine, the active form of iodide. This process occurs in the colloid and is catalyzed by membrane-bound thyroid peroxidase (TPO).
3.