Iodide Pump Iodide Trapping

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The first stage in the formation of thyroid hormones, shown in Figure 76-2, is transport of iodides from the blood into the thyroid glandular cells and follicles. The basal membrane of the thyroid cell has the specific ability to pump the iodide actively to the interior of the cell. This is called iodide trapping. In a normal gland, the iodide pump concentrates the iodide to about 30 times its concentration in the blood. When the thyroid gland becomes maximally active, this concentration ratio can rise to as high as 250 times. The rate of iodide trapping by the thyroid is influenced by several factors, the most important being the

Figure 76-1

Microscopic appearance of the thyroid gland, showing secretion of thyroglobulin into the follicles.

concentration of TSH; TSH stimulates and hypophy-sectomy greatly diminishes the activity of the iodide pump in thyroid cells.

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Essentials of Human Physiology

Essentials of Human Physiology

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