How do thyroid follicles contribute to the structure of the thyroid gland?

The thyroid gland is composed of two lobes and an isthmus, which are structured internally by numerous small, globular sacs known as follicles.1

These follicles are the fundamental functional units of the gland and contribute to its structure in the following ways:

• Lining: Each follicle is lined with follicular cells, which are responsible for synthesizing the prohormone thyroglobulin and managing the release of thyroid hormones.1
• Storage: The interior of the follicle contains a fluid called colloid, which serves as a storage medium for thyroglobulin.1

When the body requires thyroid hormones, the follicular cells reabsorb thyroglobulin from the colloid, process it into thyroxine (T4) and triiodothyronine (T3), and release these hormones into the circulatory system.1