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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 ...
. 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 the ...
. 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.


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 The basement membrane is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tissues including mesothelium an ...
, which surrounds the entire follicle.


Development

Parafollicular cells are derived from pharyngeal
endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
. Embryologically, they associate with the ultimobranchial body, 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
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 the ...
, 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 Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and va ...
,
somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-cou ...
or CGRP. 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.


See also

*
List of human cell types derived from the germ layers This is a list of cells in humans derived from the three embryonic germ layers – ectoderm, mesoderm, and endoderm. Cells derived from ectoderm Surface ectoderm Skin * Trichocyte * Keratinocyte Anterior pituitary * Gonadotrope * Corti ...


References


Further reading

* * * * * *


External links

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