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How are calcium levels levels controlled in the blood?

CaSR Controls Calcium

CaSR stands for calcium sensing receptor and they are mainly found in 4 different places:

  • Parathyroid chief cells
    • Ca binds to CaSR on chief cells
      • Causing decreased synthesis of PTH
      • PTH stands for parathyroid hormone which is produced by the parathyroid gland
        • PTH increases resorption at the bones
        • PTH increases Ca reabsorption at the kidneys
        • PTH increases synthesis of 1a-hydroxylase which produces active vitamin D in the kidneys
    • When Ca increases, PTH decreases
  • Proximal tubule of kidney
    • Ca binds to CaSR in kidney
      • Causing inhibition renal Ca reabsorption in the thick ascending limb of the loop of Henle = higher urinary Ca losses
      • Impairs ability to concentrate urine = higher water losses (if hypercalcemia persists = nephrogenic diabetes insipidus, which can progress to shock!)
  • Bone – osteoblasts and osteoclasts
    • Ca binds to CaSR on osteoblast
      • Increase osteoblast activity – increased bone building from increased Ca in blood
    • Ca binds to CaSR on osteoclast
      • Decrease osteoclast formation and activity
  • Thyroid C cells
    • Ca binds to CaSR on C cells of thyroid
      • Causes release of calcitonin which has minor effects of Ca levels
        • Increases renal Ca excretion
        • Inhibits 1a-hydroxylase in kidneys
        • Inhibits osteoclasts which break down bone and release Ca into serum