Parathyroid chief cell
| Parathyroid chief cell | |
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Micrograph of a parathyroid gland. H&E stain.
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| Identifiers | |
| Code | TH H3.08.02.5.00002 |
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Anatomical terminology
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Parathyroid chief cells (also called parathyroid principal cells or simply parathyroid cells) are one of the two cell types of the parathyroid glands, along with oxyphil cells. The chief cells are much more prevalent in the parathyroid gland than the oxyphil cells. It is perceived that oxyphil cells may be derived from chief cells at puberty, as they are not present at birth like chief cells.
Chief cells appear as a dark purple in an H&E stain, with the oxyphil cells staining as a lighter pink.
They are polygonal in shape with a round nucleus.
The chief cells play a large role in the endocrine system, as they secrete parathyroid hormone (PTH), which is involved in calcium homeostasis. PTH is an 84-amino acid hormone, initially synthesized as 115- amino acid preproPTH. PTH is further received by the calcium-sensing receptor (CaR), triggering the calcium pathway.
Chief cells spend most time inactive due to normal calcium level conditions. These inactive cells are classified as cuboidal. They have low levels of secretory granules, as opposed to active chief cells. These granules can contain acid phosphatase. Acid phosphatase is only found in larger secretory granules, 400 to 900 nm in diameter, and is less prevalent in smaller granules. This acid phosphatase is also present in the Golgi apparatus of the chief cell. However, the Golgi apparatus areas associated with parathyroid hormone packaging contained little or no acid phosphatase. 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. The electron density is caused by the secretory granules. The chief cell is thought to have a clear cytoplasm.
The secretion of PTH is regulated by the interaction of the calcium-sensing receptor with calcium in the blood. The calcium-sensing receptor is present on the plasma membrane of the chief cells. The CaR is a G protein-coupled receptor, as part of the C family. The CaR is divided into three general domains. These include an NH2- terminal extracellular end, a COOH-terminal intracellular end, and seven transmembrane domains. The CaR interacts positively with phospholipase C (PLC) and adenylyl cyclase. The CaR includes phosphorylation sites for protein kinase C (PKC) and protein kinase A (PKA). The phosphorylation of the PLC is seen to inhibit the secretion of PTH due to high calcium levels in the blood. The function of the PKA sites is currently unknown.
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