Calcium-sensing receptors respond to abnormally low levels of blood calcium and release hormones as part of a homeostatic process.
Parathyroid hormone (PTH) is secreted by the chief cells of the parathyroid gland and is a peptide hormone. The release of parathyroid hormone (PTH) affects blood calcium levels.
PTH binds to osteoblasts. This binding stimulates osteoblasts to increase their expression of RANKL, leading to stimulation of osteoclast precursors to fuse. This forms new osteoclasts, which ultimately enhances bone resorption.
The calcium released by bones being broken down raises blood calcium levels from the previously low amount.
Parathyroid hormone also activates vitamin D by promoting the activity of an enzyme that converts inactive vitamin D to active vitamin D.
Vitamin D increases the absorption of calcium from the small intestine by modulating the expression of transport proteins.
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