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Parafollicular cells, also called C cells, are neuroendocrine cells in the thyroid. They are called C cells because the primary function of these cells is to secrete calcitonin. [1] 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.
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 [5] in the ultimopharyngeal body. [6] It acts to reduce blood calcium (Ca 2+), opposing the effects of parathyroid hormone (PTH). [7]
It is composed of 116 amino acids and is produced by parafollicular cells (C cells) of the thyroid and by the neuroendocrine cells of the lung and the intestine. The level of procalcitonin in the blood stream of healthy individuals is below the limit of detection (0.01 μg/L) of clinical assays. [3]
The basolateral membrane of follicular cells contains thyrotropin receptors which bind to thyroid-stimulating hormone (TSH) found circulating in the blood. Calcitonin -producing parafollicular cells are also found along the basement membrane of the thyroid follicle, interspersed between follicular cells; and in spaces between the spherical ...
The sensors for the second are the parafollicular cells in the thyroid gland. The parathyroid chief cells secrete parathyroid hormone (PTH) in response to a fall in the plasma ionized calcium level; the parafollicular cells of the thyroid gland secrete calcitonin in response to a rise in the plasma ionized calcium level.
The ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormone can bind. Hormone receptors are dynamic structures. Changes in the number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones.
Parietal epithelial cell (PEC) Podocyte; Angioblast → Endothelial cell; Mesangial cell. Intraglomerular; Extraglomerular; Juxtaglomerular cell; Macula densa cell; Stromal cell → Interstitial cell → Telocytes; Kidney proximal tubule brush border cell; Kidney distal tubule cell; Connecting tubule cells; α-intercalated cell; β-intercalated ...
The chief cells become active in response to low calcium in the blood. The low level is sensed by the calcium- sensing receptor. These active cells have a greater electron density than the inactive chief cells. [6] The electron density is caused by the secretory granules. The chief cell is thought to have a clear cytoplasm. [7]