<prompt> All of the following are true about osteoclasts exceptDerived from monocytesPTH acts directly on osteoclastsAssociated with bone demineralisationCan phagocytose foreign bodies  <response>: Ans b: PTH acts directly onosleoclasts Ref: Harrisson 17th edition p 2367OsteoblastsSynthesize secrete matrixMesenchymal originSeen on surface of new boneOsteoblast derived matrix when mineralized is osteocyteMineralisation depends on osteoblast derived ALP marker of blastControls1. CBFA1 Runx 2- Transcription factor regulating osteoblast function. Heterozygous inactivating mutation Icleidocranial dysplasia2 Indian hedgehog3 Wnt family members. Deficiency of Wnt family co receptor LRP 5- osteoporosis4 TGF beta, FGFs 2 18, PDGF, IGF 1 25 PTH l,25 dihydroxyD activate receptors expressed by osteoblastOsteoclastResorption of boneMultinucleated giant cell 2-5nuclei from monocytemacrophage lineage.Macrophage colony stimulating factors M-CSF plays a crucial role Osteoblasts control osteoclast activityRANK ligand expressed over osteoblast progenitor stromal cells bind to RANK receptor on osteoclast progenitor to stimulate osteoclast differentiation.Osteoprotegerin binds to RANK ligand and inhibit osteoclast differentiation1L 18 is also an inhibitor of osteoclast differentiationPTH 1,25 dihydroxyD increases osteoclast number activityEstrogen decreases osteoblast number and activityBoth indirectly through RANK L and M CSF.Calcitonin has direct inhibitory effect on osteoclast formation 