How does PTH increase blood Ca 2 + levels? A.) by increasing osteoblasts activit

Question

How does PTH increase blood Ca2 + levels? A.) by increasing osteoblasts activity B.) by increasing renal excretion of Ca 2+ C.) by decreasing renal excretion of HPO42- D.) by decreasing renal production of calcitriol E.) All of these are correct How does PTH increase blood Ca2 + levels? A.) by increasing osteoblasts activity B.) by increasing renal excretion of Ca 2+ C.) by decreasing renal excretion of HPO42- D.) by decreasing renal production of calcitriol E.) All of these are correct D.) by decreasing renal production of calcitriol E.) All of these are correct

Explanation / Answer

      A.) by increasingosteoblats activity.            PTH binds to osteoblast which stimulates osteoclasts toincrease theirexpression of RANKLwhich can bind to             osteoclastprecurssor containing RANK which is a receptor forRANKL.            This binding stimulates these precurssors to fuse formingosteoclasts which ultimately enhances resorption ofbone.             Henceby increasing osteoblast activity PTH increases bloodCa+2 levels.       PTH enhances resorption ofCa+2 and Mg+2 from distaltubules.       As bone is degraded bothCa+2 and PO4- are released.       This also greatlyincreases theexcretion ofPhosphate with net loss in plasma phosphateconcentration.       By increasing the Ca+2: Kratio more Ca+2is free in the circulation.       Hence the option B and Care ruled out.       Vitamin D is also known ascalcitriol. The activated form of this vitamin increases the absorption ofCa+2.       So by decreasing theproduction of renal calcitriol PTH does not increaseCa+2.       Hence option D is ruledout.       Hence option D is ruledout.

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