Bone marrow - nonneoplastic

Author: Dragos Luca, M.D. (see Authors page)

Revised: 10 July 2018, last major update September 2012

Copyright: (c) 2002-2018,, Inc.

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

Cite this page: Luca, D. Osteoclasts. website. Accessed July 16th, 2018.
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

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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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Osteoclast resorbing bone