Question

Once inside the follicular epithelial cell, the negatively charged iodide cannot diffuse back into the interstitial fluid; this is known as ____________.

A. iodide trapping
B. endocytosis
C. pendrin
D. colloid

Answer 1

Iodide trapping refers to the active transport of iodide ions into thyroid follicular cells, where their concentration increases to facilitate thyroid hormone synthesis.

Step-by-step explanation:

The process by which follicular epithelial cells of the thyroid gland actively transport iodide ions from the bloodstream into the cell, resulting in a concentration inside the cell much higher than in the surrounding interstitial fluid or bloodstream, is known as iodide trapping.

Once inside the follicular cells, iodide ions cannot easily diffuse back out into the interstitial fluid because they are negatively charged and the hydrophobic interior of the cell membrane does not allow for the free diffusion of charged particles.

Additionally, the active transport process ensures a high intracellular concentration of iodide for the synthesis of thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). The iodide is subsequently oxidized and attached to tyrosine amino acids in thyroglobulin within the colloid to form the essential hormones.