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What will happen if there were a high concentration of both calcitonin and PTH (parathyroid hormone) in the blood? In that case, will calcium resorption from bone occur, or absorption from intestine, or deposition of calcium in bones? Also, will blood calcium level rise or fall?

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  • $\begingroup$ It depends on duration of PTH , whether its intermittent or chronic hyperparathyroidism, in different cases effects will be different. $\endgroup$ – JM97 Jul 21 '17 at 11:11
  • $\begingroup$ Thanks @David for all your effort in improving this post. Your comments were flagged for deletion and the mods did so. However, they were quite helpful and if you feel they should stay in place, let me know. Cheers. $\endgroup$ – AliceD Jul 23 '17 at 22:27
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    $\begingroup$ To OP, is this a homework question? You are required to show prior research effort. We're not here to spoonfeed the answers to your assignments. $\endgroup$ – AliceD Jul 23 '17 at 22:29
  • $\begingroup$ @AliceD This aint homework. I was reading this in book and question spoofed in my mind. There was no where to research properly. The two hormones works on different osteocytes, I had no such idea, to search anything relevant. $\endgroup$ – Anubhav Goel Jul 24 '17 at 6:55
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Short Answer: quite surprisingly, both will occur.

Long Answer: as is quite well known, calcitonin lowers blood Ca2+ levels. It performs this task by two methods:

  • it inhibits the activity of osteoclasts in the bones (Custoff, 2008)

  • it inhibits reabsorption of Ca2+ in renal tubular cells, allowing it to be excreted in urine (Potts et al, 2008)

However, the second mechanism is only minor. On the other hand, parathyroid hormone (PTH) performs just its opposite: it increases Ca2+ levels in the blood.

So, lets come to the main point: since calcitonin and PTH have opposing functions, what would happen if both were acting simultaneously?

It seems, funnily though, that both the functions will occur simultaneously. Wong et al, 1975, in their research, showed that the target cells of calcitonin and PTH are different i.e. calcitonin and PTH act on different osteoclasts. So, to put it simply, while activity of some osteoclasts would be decreased, that of some others would be increased. Overall, Ca2+ levels in the blood would remain pretty much constant.

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