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Q.why inc ALP in ostomalacia, primary hyperthyroidism....

Discussion in 'Step I' started by sgsh, Aug 2, 2015.

  1. sgsh

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    In kaplan, endocrinology (in the chapter-Hormonal control of calcium and phosphate), it's mentioned that -Increased alkaline phosphatase is associated with osteoblastic activity but again in FA (musculoskeletal sys) it's mentioned that in osteomalacia,rickets.primary hyperthyroidism and paget's disease, ALP increases where osteoclastic activity is dominant according to what I know. so, it's really contradicting kaplan from FA and I am really confused. Can anybody pls help me out -what is the cause of increaed ALP in the above conditons mentioned.Thanks a lot.
     
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  3. Macaroon_Berry

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    I'll try to explain it the best way I can: osteoclasts activity breaks down the bone to release calcium and phosphate into the serum. Parathyroid hormone released in response to low serum calcium (as in osteomalacia & rickets where you have vitamin D deficiency and thus decreased calcium re-absorption) as well as in hyperparathyroidism will cause elevated parathyroid hormone whose receptor is on OSTEOBLASTS which will then cause these osteoblasts to release osteoclasts activating factor thus activating OSTEOCLASTS.
    You are correct in stating that ALP is an indicator of osteoblast activity, but as you can see in these conditions you mentioned, even though there's primarily osteoclast activity, the mechanism is via parathyroid hormone directly acting on osteoblasts in order to activate osteoclasts. So parathyroid hormone activates osteoclasts indirectly.

    Do you understand why ALP is an indicator of osteoblast activity? Osteoblasts lay down osteoid (which is NOT bone). This osteoid must become mineralized with calcium in order to become bone, however to mineralize the osteoid you need an alkaline environment which is produced by ALP activity.
     
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  4. sgsh

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  5. sgsh

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    Thanks a million for your superb explanation. You expressed this tough mechanism in way that is easy to grasp and understand.It cleared my doubts.Thanks again.
     
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