Bone marrow nonneoplastic



Topic Completed: 1 September 2012

Minor changes: 14 May 2021

Copyright: 2002-2019,, Inc.

PubMed Search: Bone marrow [title] osteoclasts [title]

Dragos C. Luca, M.D.
Page views in 2020: 1,411
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Cite this page: Luca DC. Osteoclasts. website. Accessed December 3rd, 2021.
Definition / general
  • Cells derived from hematopoietic progenitor cells involved in bone resorption, primarily due to remodeling and not calcium homeostasis
  • Along endosteal surface of bony trabeculae (reside in Howship lacunae) or along margins in marrow smears
  • Common in children (active bone remodelling); in adults associated with metabolic or neoplastic diseases
  • Some overlapping immunophenotypic features with monocytes / macrophages
  • Relatively recently identified osteoclast colony stimulating factor and transcription factors involved in osteoclastogenesis
  • Activated by parathyroid hormone and by cytokines RANKL and macrophage colony stimulating factor (Arthritis Res Ther 2006;8:201)
  • Osteoclasts use their ruffled borders (with villous extensions) to bind to matrix adhesion proteins, produce resorption pits / bays (shallow concavities) called Howship lacunae
  • Plasma membrane forms a seal with bone; osteoclast acidifies extracellular area, which solubilizes the mineral and releases enzymes which dissolve the matrix
Diagrams / tables

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Cross section

Bone resorptive cycle

Microscopic (histologic) description
  • Very large (up to 100 microns), multinucleated (2 - 12 nuclei) giant cells associated with bone surface
  • Abundant, blue purple pale pink cytoplasm containing many fine, red purple granules
  • Also contain bone sand in the cytoplasm
  • Multiple, relatively uniform but widely separated nuclei, each with one nucleolus and dense chromatin
  • Generally, less mature osteoclasts have basophilic cytoplasm and mature forms have brightly eosinophilic cytoplasm
Microscopic (histologic) images

AFIP images

Very large cell with multiple
nuclei with distinct nucleoli,
cytoplasm has coarse
azurophilic granules

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Electron microscopy description
  • Numerous mitochondria, rare lysosomes
  • Ruffled edge in area of cell membrane is associated with bone resorption
Electron microscopy images

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