Bone
General
Histology

Author: Nat Pernick, M.D. (see Authors page)

Revised: 3 October 2016, last major update June 2005

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Bone histology[title]
Cite this page: Histology. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/bonehistology.html. Accessed December 10th, 2016.
Definition / General
  • Bone: mineralized osteoid; either lamellar bone or woven bone (see below)
Diagrams / Tables
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Cortical bone

CEMENT LINE
General
  • Junction between original resorbed surface and new bone
  • Sharp and basophilic with routine staining
  • Also called reversal front

LAMELLAR BONE
General
  • Layered bone with concentric parallel lamellae
  • Gradually replaces woven bone
  • Normal type of bone found in adult skeleton
  • Stronger than woven bone

OSTEOBLASTS
General
  • Arise from marrow mesenchymal cells
  • When active, are plump and present on bone surface
  • Eventually are encased within the collagen they produce and get flattened (see osteocytes below)
  • Have a perinuclear halo resembling plasma cells in cytologic preparations due to prominent Golgi zone
  • Synthesize and transport collagenous matrix, initiate and regulate mineralization, control removal of bone via osteoclasts, express Vitamin D receptors
  • Activity is promoted by physical activity (Wolf’s law)
  • Express parathormone receptors (mediates the activation of osteoclasts)
  • Osteoblasts control osteoclast activity via parathyroid hormone (parathormone), PHRP (Parathyroid hormone related protein), IL1, TNF alpha; digestion of bone by osteoclasts releases cytokines and growth factors for osteoblasts
  • Express parathormone receptors (mediate the activation of osteoclasts)

Micro images
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    Osteoblasts and osteoclasts


Positive stains
  • Alkaline phosphatase, estrogen receptors, parathyroid hormone

Electron microscopy description
  • Resemble fibroblasts due to well developed rough endoplasmic reticulum and Golgi

OSTEOCLASTS
General
  • Cause bone resorption due primarily to remodeling and not calcium homeostasis
  • Derived from monocyte fusion
  • Multinucleated (2-12 nuclei) giant cells, associated with bone surface
  • Use their ruffled borders (with villous extensions) to bind to matrix adhesion proteins, produce resorption pits/bays (shallow concavities) called Howship’s lacunae
  • Plasma membrane forms a seal with bone
  • Osteoclast acidifies extracellular area, which solubilizes the mineral and releases enzymes which dissolve the matrix
  • Contains tartrate resistant acid phosphatase

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    Osteoclasts


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

OSTEOCYTES
General
  • The mature form of osteoblasts after they are surrounded by matrix
  • Ruffled edge in area of cell membrane is associated with bone resorption
  • May maintain serum calcium and phosphorus levels
  • Can translate mechanical forces into biologic activity

Drawings
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    Osteocytes


Micro images
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    Osteocyte


OSTEOID
General
  • Non mineralized bone always present at the formative surface of bone, but usually a very thin layer
  • Resembles hyalinized collagen
  • Composed of type I collagen (90%), acid mucopolysaccharides, noncollagen proteins including bone morphogenetic protein (may initiate bone formation), adhesion proteins (fibronectin, osteopontin, thrombospondin), calcium binding proteins (osteonectin, bone sialoprotein), mineralization proteins (osteocalcin), enzymes (collagenase, alkaline phosphatase)
  • Increased if increased bone formation (fracture callus, Paget's disease, hyperparathyroidism), if inadequate mineralization or if toxic / inhibitory structures present in bone (aluminum, iron, fluoride)

OSTEON
General
  • Dense compact cylindrical unit underlying cortical bone
  • Formed in childhood by ingrowth of periosteal vessels that follow a cutting cone of osteoclasts through the cortex
  • Tunnel is haversian canal, is filled in partially with osteoblast created bone matrix

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    Haversian systems


OSTEOPROGENITOR CELLS
General
  • Mesenchymal stem cells near bony surfaces, can produce osteoblasts

PERIOSTEUM
General
  • Outer fibrous layer and inner cellular (cambium) layer of osteoprogenitor cells (fibroblasts and osteoclasts)
  • Contains nerve fibers, Sharpey’s fibers/perforating collagenous fibers that penetrate outer layer of bone
  • May become detached from bone due to benign or malignant processes, causing new bone formation between elevated periosteum and bone and producing radiologic changes

Drawings
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    Perforating fibers


TETRACYCLINE
General
  • Binds to actively mineralizing surfaces and fluoresces in ultraviolet light

WOVEN BONE
General
  • Immature (streamer) bone due to haphazard (random) arrangement of collagen fibers, found during growth, healing, repair, infections or in some neoplasms
  • Highlighted with polarized light or reticulin stain
  • Abnormal in adults and associated with fibrous dysplasia or other causes of accelerated bone turnover

BONE HISTOMORPHOMETRY
General
  • Measuring bone formation (% active osteoblastic surface, % osteoid surface, % mineralizing surface), bone mineralization (osteoid volume, mineral apposition rate), bone resorption (% total eroded surface, % active osteoclastic surface)
  • Bone resorption is identified by numerous osteoclasts in Howship’s lacunae and in bone margins

BASIC MULTICELLULAR UNIT
General
  • To fulfill the biological requirements, bone needs to continuously renew itself, which it does at multiple sites called basic multicellular units (BMUs)
  • Bone resorption is identified by numerous osteoclasts in Howship’s lacunae and in bone margins
  • Cyclic events involving matrix resorption and formation occur in these BMUs, i.e., activation of osteoprogenitor cells to proliferate and differentiate (A), resorption of bone matrix by osteoclasts (R), quiescent phase for reversing resorption to formation (R) and the formation of bone matrix by osteoblasts (F)
  • The cellular activities are coupled within each BMU’s remodeling cycle, i.e., A-R-FBone is modeled to reach peak bone mass; then 5-10% is remodeled per year in these BMUs