Which statement correctly identifies the storage location of thyroid hormones within the thyroid follicle?

Which statement correctly identifies the storage location of thyroid hormones within the thyroid follicle?

• A. Epithelial cell wall of the follicle
• B. Colloid in the follicle
• C. Isthmus of the thyroid gland
• D. Extracellular space of the thyroid gland

Answer: (B)

The main idea is that thyroid hormones are stored in the colloid inside the follicular lumen. Thyroglobulin, produced by the follicular cells, is secreted into this colloid and becomes iodinated in place; the bound hormones (as part of thyroglobulin) are stored there until needed. When TSH signals, the colloid is endocytosed and proteolyzed to release free T3 and T4 into circulation. So the storage location is the colloid within the follicle, not the epithelial cell wall, the isthmus, or the extracellular interstitial space of the gland.

The main idea is that thyroid hormones are stored in the colloid inside the follicular lumen. Thyroglobulin, produced by the follicular cells, is secreted into this colloid and becomes iodinated in place; the bound hormones (as part of thyroglobulin) are stored there until needed. When TSH signals, the colloid is endocytosed and proteolyzed to release free T3 and T4 into circulation. So the storage location is the colloid within the follicle, not the epithelial cell wall, the isthmus, or the extracellular interstitial space of the gland.