This presentation provides a detailed overview of the classical histology of the thyroid gland, emphasizing its unique and easily identifiable structure. The tissue is characterized by epithelial-lined follicles (small cysts) filled with pinkish, inspissated colloid, noting the considerable variation in follicle size. The surrounding interfollicular connective tissue is highly vascularized with a capillary plexus. The presentation differentiates between the two primary cell types and their hormonal products: the follicular cells, which produce and store the metabolic hormones T3 and T4, and the parafollicular cells (C cells or light cells), which are located between the follicles and produce calcitonin (thyrocalcitonin). The appearance of these distinct, endocrine-looking parafollicular cells is visually identified and described.
Summarizing the Histology of the Thyroid Gland
0:04 Classical Thyroid Tissue: The thyroid gland has a highly distinctive appearance in the body, which is rarely mimicked (exceptions include inflamed kidney tubules, severely lactating breast lobules, or small colloid follicles in the pituitary intermediate lobe).
0:41 Follicle Structure: The thyroid is defined by epithelial-lined spaces or small cysts (follicles) filled with pinkish, inspissated colloid. The size of these follicles shows considerable variation.
1:13 Follicular Epithelium: Every colloid follicle is lined by a simple, non-stratified, relatively cuboidal epithelium.
1:31 Interfollicular Tissue: The connective tissue surrounding the follicles is extremely vascular, featuring a rich plexus of capillaries.
2:02 Hormonal Production (T3/T4): The follicular cells create thyroid hormone (T3 and T4), which is the storage form of the hormone, retained inside the follicle.
2:25 Second Hormone (Calcitonin): The thyroid produces a second hormone, thyrocalcitonin (calcitonin), which is crucial for calcium regulation.
2:40 Parafollicular Cells (C Cells): Calcitonin is produced by parafollicular cells (also called C cells or light cells), which are located in the spaces between the follicles.
3:44 Identifying Parafollicular Cells: These cells appear as typical endocrine cells, often in clusters, featuring a round nucleus and slightly pinkish cytoplasm, distinct from both the follicular cells and the surrounding connective tissue.
5:02 Key Takeaway: The thyroid gland is the master metabolic gland of the body, producing T3/T4 (follicular cells) and Calcitonin (parafollicular cells).