Parafollikulære

Parafollikulære cells, also known as C cells, are a population of neuroendocrine cells located in the thyroid gland. They reside in the parafollicular region, typically in the interfollicular spaces between thyroid follicles. These cells originate from neural crest cells and migrate into the thyroid during development.

The principal product of parafolikulular cells is calcitonin, a peptide hormone that helps regulate calcium homeostasis. Calcitonin lowers blood calcium levels by inhibiting osteoclast-mediated bone resorption and reducing calcium release from bone tissue. In humans, the exact physiological role of calcitonin is less critical than that of parathyroid hormone and vitamin D, but calcitonin secretion remains an important diagnostic and research marker.

Histologically, C cells are smaller than follicular cells and contain characteristic dense-core secretory granules that store calcitonin. They can be identified in tissue sections by immunohistochemical staining for calcitonin.

Clinical significance is most prominently related to neoplasia. Medullary thyroid carcinoma (MTC) arises from parafolikulære cells and typically secretes calcitonin and other peptides. Serum calcitonin, sometimes measured alongside carcinoembryonic antigen (CEA), is used in the diagnosis and monitoring of MTC. MTC is associated with germline RET mutations in multiple endocrine neoplasia (MEN) syndromes. C-cell hyperplasia can also occur and may precede MTC in hereditary forms.

In summary, parafolikulære cells are the thyroid’s C cells, neuroendocrine in origin, producing calcitonin and contributing to the gland’s neuroendocrine component.