Parafollicular cells, also called C cells, are

neuroendocrine cell Neuroendocrine cells are cells that receive neuronal input (through neurotransmitters released by nerve cells or neurosecretory cells) and, as a consequence of this input, release messenger molecules (hormones) into the blood. In this way they bri ...

s in the

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...

. The primary function of these cells is to secrete

calcitonin Calcitonin is a 32 amino acid peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid (or endostyle) in humans and other chordates. in the ultimopharyngeal body. It acts to reduce blood calcium (Ca2+), opposing th ...

. They are located adjacent to the thyroid follicles and reside in the connective tissue. These cells are large and have a pale stain compared with the follicular cells. In

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

and avian species these cells occupy a structure outside the thyroid gland named the

ultimobranchial body The ultimopharyngeal body, or ultimobranchial body or ultimobranchial gland is a small organ found in the neck region of many animals. In humans, it develops from the fourth pharyngeal pouch into the parafollicular cells of the thyroid to produc ...

Structure

Parafollicular cells are pale-staining cells found in small number in the thyroid and are typically situated basally in the epithelium, without direct contact with the

follicular lumen The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...

. They are always situated within the basement membrane, which surrounds the entire follicle.

Development

Parafollicular cells are derived from pharyngeal endoderm. Embryologically, they associate with the

, which is a ventral derivative of the fourth (or fifth) pharyngeal pouch. Parafollicular cells were previously believed to be derived from the

neural crest Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...

based on a series of experiments in quail-chick chimeras. However, lineage tracing experiments in mice revealed that parafollicular cells are derived from the endoderm origin.

Function

Parafollicular cells secrete

, a hormone that participates in the regulation of

calcium metabolism Calcium metabolism is the movement and regulation of calcium ions (Ca2+) ''in'' (via the gut) and ''out'' (via the gut and kidneys) of the body, and ''between'' body compartments: the blood plasma, the extracellular and intracellular fluids, and ...

. Calcitonin lowers blood levels of calcium by inhibiting the resorption of bone by

osteoclast An osteoclast () is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated pro ...

s, and its secretion is increased proportionally with the concentration of calcium. Parafollicular cells are also known to secrete in smaller quantities several neuroendocrine peptides such as serotonin, somatostatin or

CGRP Calcitonin gene-related peptide (CGRP) is a member of the calcitonin family of peptides consisting of calcitonin, amylin, adrenomedullin, adrenomedullin 2 ( intermedin) and calcitonin‑receptor‑stimulating peptide. Calcitonin is mainly produc ...

. They may also have a role in regulating thyroid hormones production locally, as they express

thyrotropin-releasing hormone Thyrotropin-releasing hormone (TRH) is a hypophysiotropic hormone produced by neurons in the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) and prolactin from the anterior pituitary. TRH has been used clinicall ...

Clinical significance

When parafollicular cells become cancerous, they lead to

medullary carcinoma Medullary carcinoma may refer to one of several different tumors of epithelial origin. As the term " medulla" is a generic anatomic descriptor for the mid-layer of various organ tissues, a medullary tumor usually arises from the "mid-layer tissues ...

of the thyroid.

References

External links

* * * * {{Authority control Peptide hormone secreting cells Human cells Thyroid