Parafollicular cell

Inhibition of calcitonin secretion from thyroid parafollicular cells... 

Calcitonin. This hormone, which is also secreted from the thyroid gland, is synthesized by the parafollicular cells (C cells) located between the follicles. The primary effect of calcitonin is to decrease the blood levels of calcium and phosphate. The mechanism of action involves the direct inhibition of osteoclast activity, which decreases bone resorption. This results in less demineralization of the bone and therefore a decrease in the release of calcium and phosphate from the bone into the blood. Calcitonin has no direct effect on bone formation by osteoblasts. 

In most mammals, calcitonin is synthesized by specialized parafollicular cells in the thyroid. In sub-mammalian species, it is synthesized by specialized anatomical structures known as ulti-mobranchial bodies. 

Calcitonin is a single chain polypeptide of 32 amino-acids. It is secreted by the parafollicular cells of the thyroid gland. However in the circulation various forms of calcitonin are present, probably including several precursors. Calcitonin inhibits osteoclastic resorption of bone and it increases calcium and... 

The hormone that opposes the action of PTH is CT. It is produced in the parafollicular cells of the thyroid gland, whereas thyroxine is produced by the follicular cells. Human CT is a 32 amino acid peptide with one disulfide bond. CT is secreted in response to increased serum [Ca2+], especially following a meal. Its role is to prevent hypercalcemia by decreasing the serum [Ca2+]. This is achieved by counteracting the action of PTH on osteoclasts while having no effect on osteoblasts. In addition, CT affects the movement of serum Ca2+ into a labile Ca pool on the bone surface, which then releases Ca back into the circulation when [Ca2+] in serum declines. 

Calcitonin (ihyrocalcilonin) is a 32-amino-acid polypeptide hormone secreted by parafollicular cells of the thyroid glands in response lo hypocalcemia. The entire 32-residue peplide appears to be required for activity, bccau.se smaller fragments are totally inactive. Common structural features of calcitonin isolated fntm different species are a COOH-lerminal prolinamide. a disulfide bond between residues I... 

The follicle cells, called thyrocytes, produce the thyroid hormones and are derived from the entodermal pharynx. Interspersed between follicles are specialized APUD cells derived from the neural crest, called C-cells or parafollicular cells. These cells produce calcitonin (CT), a polypeptide hormone discussed in Chapter 37. 

Calcitonin A polypeptide honnone of 32-amino acid residues that is synthesized in the parafollicular cells (C cells) of the thyroid gland. Calcitonin is seaeted in response to elevated blood Ca levels. 

Ljungberg O, Bondeson L, Bondeson AG. Differentiated thyroid carcinoma, intermediate type A new tumor entity with features of follicular and parafollicular cell carcinomas. Hum Pathol. 1984 15 218-228. 

Sensory neurons Cholinergic neurons Adrenergic neurons Rohon-Beard cells Satellite cells Schwann cells Glial cells Parafollicular cells Calcitonin producing cells... 

The majority of the thyroid giand contains follicular cells responsible for the production of the thyroid hormones. A second population of endocrine cells within the thyroid known as C (clear) cells, or parafollicular cells, produce the hormone calcitonin (CT), which has an opposing action to that of PTH in that it decreases the Ca concentration in body fluids. It accomplishes this by inhibiting the activity of osteoclasts (i.e., decreasing Ca release from bone by inhibiting bone resorption). The actual biosynthesis and release of CT is regulated by the concentration of Ca in plasma (i.e., when it is high, CT secretion increases). 

Parafollicular cells, also called light cells or C cells, are located individually or in clusters between follicular cells but do not border on the colloid. These cells produce ... 

C call (parafollicular cell) Anyone of a group of calcium-secreting cells in vertebrates that are derived from the terminal pair of gill pouches. In mammals these cells are incorporated into the thyroid gland and the parathyroid gland. 

Contrary to PTH, calcitonin has a lowering action on blood Ca activity. It is synthesized in the parafollicular cells (C cells) in the thyroid. An increased blood Ca activity leads to calcitonin secretion, and within a few minutes both calcium and phosphate concentrations in plasma are lowered. This effect is accomplished by an effect on the bone cells, where calcium is bound as hydroxyapatite. Besides this effect, calcitonin also decreases intestinal uptake and renal reabsorption. Calcitonin inhibits the osteoclasts ( bone eater cells ) and hence reduces the amount of calcium and phosphate released from bone to the extracellular fluid. The effect on the kidneys leads to an increased excretion of calcium, phosphate, sodium, chloride, and water. 

Autoradiographs taken many hours after injection of the labelled compound and containing areas of high localisation may indicate retention of a metabolite. Thus, 24 hours after injection of labelled 5-hydroxytryptophan (5-HTP), there is a pronounced retention of radioactivity in the thyroid which is confined to the parafollicular cells [131], As no free amino acid is demon-trable biochemically at this time, then the radioactivity points to the presence of serotonin (5-HT) which is known to be present in these cells [132, 133]. 

Inhalable co-spray dried powders of salmon calcitonin-loaded chitosan nanoparticles with mannitol have been prepared and analyzed. Salmon calcitonin or Calcitonin (also known as thyrocalcitonin) is a 32-amino acid linear polypeptide hormone that is produced in humans primarily by the parafollicular cells (also known as C-cells) of the thyroid, and in many other animals in the ultimobranchial body. It acts to reduce blood calcium (Ca ), opposing the effects of parathyroid hormone (PTH) [118]. The... 

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