NBME 21 Paracrine stimulation of osteoclasts by osteoblasts (NBME Answers)

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Retired NBME 21 Answers

nbme21/Block 4/Question#31 (reveal difficulty score)
A 48-year-old woman comes to the physician ...
Paracrine stimulation of osteoclasts by osteoblasts 🔍 / 📺 / 🌳 / 📖
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Hyperparathyroidism causing bone lesions is via Osteoblasts increasing RANK -L expression to bind to RANK on Osteoclasts and stimulating them ---> inc Bone Resorption

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pg32 Picked D despite understanding the above ^^ because IL-1 is also known as osteoclast acitivating factor... +8

plzhelp123 ^ I did the same, but it appears that IL-1 activates osteoclasts in multiple myeloma. Which makes sense as that is a neoplasm of immune cells which can produce interleukins. +

caitlyncloy can anyone explain why this the answer is "PARACRINE" stimulation?? I rule out the correct answer because i was picturing RANK and RANK L binding, which is not paracrine?! +1

caitlyncloy oh.. it seem RANK L is secreted to activate the clasts.. i was picturing it as RANKL was on the surface of the blast. reference: https://www.youtube.com/watch?v=hOIBRJeetAs +1

makingstrides If you can, I Would highly recommend looking at the sketchy pharm for this. It explains this well, in my opinion, and definitely helped me. +

jatsyuk38 Goljan I could've sworn said PTH stimulates osteoblasts to secrete IL-1 to activate osteoclasts. He also said estrogen prevents osteoporosis by inhibiting osteoblast release of IL-1...however there is also a UWorld question where it said RANK-L plays a more important role actor (over IL-1) in PTH mediated bone breakdown +1

Primary hyperparathyroidism: overproduction of PTH by parathyroid chief cells Effect of PTH on bone → increased bone resorption → ↑ release of calcium phosphate → ↑ calcium levels Induces RANKL expression in osteoblasts → binding of RANKL to RANK on osteoclasts → activation of osteoclasts Induces IL-1 expression in osteoblasts → activation of osteoclasts" Amboss

Not sure why D is wrong

+/- alexv0815(10)

Primary hyperparathyroidism: overproduction of PTH by parathyroid chief cells Effect of PTH on bone → increased bone resorption → ↑ release of calcium phosphate → ↑ calcium levels

Induces RANKL expression in osteoblasts → binding of RANKL to RANK on osteoclasts → activation of osteoclasts

Induces IL-1 expression in osteoblasts → activation of osteoclasts

Not sure why D is wrong

+6/- alexv0815(10)

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