What is the Difference Between Thyroid Follicle and Colloid

The key difference between thyroid follicle and colloid is that thyroid follicle secretes thyroid hormones while colloid is the fluid found inside the thyroid follicle.

The thyroid gland is an endocrine gland. It lies in the anterior portion of the lower neck and below the larynx. The thyroid gland secretes hormones, thyroxine and triiodothyronine, which are vital for growth and metabolism in the body. The gland consists of two lobes that lie on either side of the trachea and connect through a tissue called the isthmus. These lobes and isthmus contain small globular sacs called thyroid follicles. These follicles are filled with a fluid called the colloid.

CONTENTS

1. Overview and Key Difference
2. What is Thyroid Follicle  
3. What is Colloid
4. Similarities – Thyroid Follicle and Colloid
5. Thyroid Follicle vs Colloid in Tabular Form
6. Summary – Thyroid Follicle vs Colloid

What is Thyroid Follicle?

Thyroid follicle is the structural and functional unit of the thyroid gland. It secretes thyroid hormones – thyroxine and triiodothyronine. The lobes of the thyroid gland and the isthmus contain small globular sacs called thyroid follicles. They are spherical in shape, and the wall comprises cuboidal epithelial cells known as follicular cells. The follicular cells form a single layer of cells, which makes the external structure of the thyroid follicle. The interior space between the follicular cells is the follicular lumen. The follicular cell membrane contains thyrotropin receptors that bind to the thyroid-stimulating hormone. Another hormone found along the basement membrane of the thyroid follicle is calcitonin-producing parafollicular cells.

The follicular cells draw iodide and amino acids from the blood. It then synthesizes thyroglobulin and thyroperoxidase and secretes them into thyroid follicles with iodide. In order for these events to take place, the thyroid follicles have a specialized and unique structure and comprise of cell-specific protein components, which include thyroglobulin, thyroid peroxidase, and Na+/I− symporter.

What is a Colloid?

The fluid that fills the thyroid follicles is called the colloid. Colloid contains prohormone thyroglobulin. The hormone production is dependent on iodide, which is an essential and unique factor for hormones. Colloid is a proteinaceous depot of thyroid hormone percussor. It is an inactive precursor of thyroxine and triiodothyronine, which are made up of glycoprotein thyroglobulin. Iodine binds to the residues of tyrosine of thyroglobulin.

The thyroid follicle lumen contains the colloid and acts as a storage for thyroid hormone. When hormones are in need, colloid reabsorbs thyroglobulin from the follicular lumen into the cells. Thyroglobulin splits into its components, which include the two hormones thyroxine and triiodothyronine. This releases the hormones, and they transport across the epithelium of follicles and release into the blood capillaries that lie adjacent to the epithelium. Abnormalities such as colloid nodules arise when one or more overgrowths occur in the normal thyroid tissue. These are benign; however, and they grow large. These colloid nodules do not spread beyond the thyroid gland.

What are the Similarities Between Thyroid Follicle and Colloid?

• Thyroid follicle and colloid are located in the thyroid gland.
• Both are involved with the production of thyroid hormones: thyroxine and triiodothyronine.
• Moreover, abnormalities in both may lead to metabolic dysfunctions.

What is the Difference Between Thyroid Follicle and Colloid?

Thyroid follicle secretes thyroid hormones, thyroxine and triiodothyronine, while colloid is the fluid found inside the thyroid follicle. Thus, this is the key difference between thyroid follicle and colloid. That is; thyroid follicle produces thyroglobulin while the colloid stores thyroglobulin. Moreover, upon staining, thyroid follicles show purple-colored cells while the colloid shows pink coloured cells.

The below infographic presents the differences between thyroid follicle and colloid in tabular form for side by side comparison.

Summary – Thyroid Follicle vs Colloid

Thyroid gland is an endocrine gland. It consists of two lobes that contain small globular sacs called thyroid follicles. Thyroid follicle secretes thyroid hormones, thyroxine and triiodothyronine, while the colloid is the fluid inside the thyroid follicle. So, this is the key difference between thyroid follicle and colloid. Thyroid follicles are simple epithelial cells. Colloid, on the other hand, is a glycoprotein-rich fluid that lies in the follicular lumen and contains the prohormone thyroglobulin.

Reference:

1. “Thyroid Colloid.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
2. “Thyroid Follicle.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Thyroid follicle cells” By CFCF – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Dermal mucinosis – colloidal iron stain” By fishhawk (CC BY 2.0) via Flickr