Osteoclasts - anabolic effects?

[Lothric]

Hey,

FA 17 says that increased rank-l from ostebolasts and osteocytes binds rank on osteoclasts, causing increased calcium ions and bone resorption.

It is also said that at low, intermittent levels, PTH exerts anabolic effects on BOTH osteoblasts and osteoclasts (indirect).

What is meant by "indirect"? Are they referring to the increased calcium ions when rank-l binds to rank? is that considered an "anabolic effect"? Note that it seems like the calcium ions are NOT from the bone resorption when they write it like they do (increased calcium ions AND bone resorption when rank-l binds to rank).

Edit: I think "indirect" here refers to the increase in calcium ions (the "anabolic effect"). The direct would be what osteoclasts are known for; their breaking down of bone. Correct me if I'm wrong!

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[iBS1972]

I'm not completely sure why they say "anabolic effects on both osteoblasts and osteoclasts".
Some background info that might help you piece it together or point you in the right direction:
--PTH directly affects osteoblast cells by: 1. promoting their survival, 2. promoting differentiation into osteoblasts, 3. increases osteoblast Rank-L expression
What has been taught to me was that PTH doesn't really have a direct role on osteoclasts, but rather indirectly stimulates them by inducing osteoblast Rank-L expression (which then binds to osteoclast Rank-L receptor).
Note: appropriate bone formation requires the balance of osteoblast AND osteoclast activity. It's better to think of it as bone REMODELING as the end-goal.

 

[Lothric]

Ah, wow. Your final note there made me understand this concept now. So the anabolic effect FA refers to is the optimal balance between osteoblasts and osteoclasts at low, intermittent levels of PTH. But when PTH is elevated the osteoclasts go all crazy --> osteitis fibrosa cystica with a dominating catabolic effect.

Thanks for the help man!