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 br ...
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 t ...
. 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 ...
. 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 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. 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 and ...
, which surrounds the entire follicle.
Development
Parafollicular cells are derived from pharyngeal
endoderm. 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, ...
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 ...
, a hormone that participates in the regulation of
calcium metabolism. 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 ...
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 pr ...
. They may also have a role in regulating thyroid hormones production locally, as they express
thyrotropin-releasing hormone.
Clinical significance
When parafollicular cells become cancerous, they lead to
medullary carcinoma of the thyroid.
See also
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List of human cell types derived from the germ layers
References
Further reading
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External links
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{{Authority control
Peptide hormone secreting cells
Human cells
Thyroid