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BONE HISTOLOGY

Ma. Minda Luz M. Manuguid M.D.

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Osseous tissue

BONE is a specialized form ofconnective tissue composed of

specialized cells (Osteocytes)enclosed within shallow depressions(lacunae) widely scattered in a tough

organic matrix in which minerals havebeen precipitated.

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characteristics

composition: 20-30% organic matter;25% water; 40-50% inorganic

matter high tensile & compressive strength relatively lightweight; has some

elasticity dynamic tissue constantly

undergoing resorption & renewal

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functions

provide (with Cartilage) mechanicalsupport & protection of other

organs especially within the skull &

thoracic cage principal internal support of the body rigid structures for attachment of

tendons & muscles --- movement;locomotion

mobilizable storage depot for Calcium marrow is hematopoietic

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Bone components

parenchymal cells: OSTEOCYTES andOSTEOPROGENITOR CELLS;OSTEOBLASTS;

OSTEOCLASTS matrix/ extracellular fibers : OSSEIN

matrix/extracellular ground substance

inorganic: (mineralized) HYDROXYAPATITEcrystals organic: OSTEOID: Glycosaminoglycans,

Glycoproteins: KERATAN SULFATE;CHONDROITIN SULFATE; HYALURONIC

ACID

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Bone cells

OSTEOPROGENITOR CELLSrelatively undifferentiated

found on all free surfaces of Boneactive during normal bone growthpale oval to elongated nucleusacidophilic to faintly basophilic cytoplasm

active during normal bone growth & duringadult reorganization

can transform into Osteoblasts

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Bone cells

OSTEOBLASTS bone-forming cells found on the

advancing surfaces of growing bone ovoid nucleus with prominent nucleolus basophilic cytoplasm with extensive ER,

many ribosomes, numerous elongatedmitochondria, & well-developed Golgi

(+) alkaline phosphatase secrete bone matrix (osteoid) converted to Osteocytes

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Bone cells

OSTEOCYTES main parenchymal cells of mature bone

flattened, found inside lacunae with numerous fine processes insidecanaliculi radiating outward,communicating with other canaliculi &

with Haversian or Volkmanns canals can still secrete osteoid but to a lesser

degree than osteoblasts

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Bone cells

OSTEOCLASTS phagocytic, bone-destroying cells

multinucleated, syncitial formed bycoalescence/fusion of severalmacrophage-type cells; may have up to50 nuclei

associated with Howshipslacunae (+) acid phosphatase

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Bone matrix

Extracellular fibers type I collagen, 50-70 nm in diameter, in

cross-linkages of 67 nm periodicity called OSSEIN bone collagen

Amorphous ground substance organic: OSTEOID: Keratan sulfate,

Chondroitin sulfate, Hyaluronic acid

inorganic: HYDROXYAPATITE crystals(Ca PO4 OH ); Ca carbonate, Mg, F, Na,Citrate; may be extracted by a weakacid/chelating agent

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Bone morphology

Gross: Long bones femur, humerus,

Flat bones skull bones Short bones carpals, tarsals, Irregular bones patella,

ossicles

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BONE MORPHOLOGY:GROSS

Periosteum - outer coveringSharpeys fibers

Epiphysis - endsEpiphyseal Plate hyaline

cartilage - region of verticalgrowth of long bones

Metaphysis - broad neck areaDiaphysis shaftMarrow CavityEndosteum inner covering

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Parts of a Long bone

DIAPHYSIS shaft thick-walled hollowcylinder of compact bone with voluminouscentral medullary cavity

EPIPHYSIS end spongy bone covered bya thin peripheral cortex of compact bone;Epiphyseal plate- cartilage betweenepiphysis & diaphysis, only seen in growingbones

METAPHYSIS columns of spongy bonewhich unite the epiphyseal plate to thediaphysis

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Bone coverings

PERIOSTEUM / PERICRANIUM outerdense irregular connective tissue; inner layerof osteoblastsSharpeys fibers- coarse bundles of

collagenous fibers from the periosteum whichturn inward to penetrate the outercircumferential lamellae, anchoring theperiosteum to the underlying bone; especiallynumerous in skull bones

ENDOSTEUM / DURA MATER thin cellularmembrane lining the marrow cavity & thecavities between trabeculae of spongy bone

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BONE MORPHOLOGY:

MICROSCOPICMicroscopic:Compact bone Substantia compacta

apparently solid/continuous but containsmicroscopic spacesCancellous/Spongy bone Substantia

spongiosa 3dimensional lattice ofbranching bony spicules/trabeculaedelimiting a labyrinthine system ofintercommunicating spaces occupied bybone marrow.

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BONE MORPHOLOGY

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BONE HISTOLOGY

COMPACT BONE:Haversian

system/OSTEONLamellae layers of

osteocytes & bone matrixHaversian canals lie

parallel to long axis ofbone

Volkmanns canals oblique/ horizontal

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BONE MORPHOLOGY:MICROSCOPIC

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Bone histology

Lamella: Haversian lamellae- concentrically

arranged lamellae around alongitudinal vascular channel: 4 20 /osteon

interstitial/angular lamellae-irregular lamellae between osteons

inner circumferential lamellae justbeneath the endosteum outer circumferential lamellae just beneath the periosteum

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Bone histology

Lacunae - lenticular cavitieshousing bone cells

Canaliculi - slender tubularpassages radiating from lacunae &penetrating the interstitialsubstance to anastomose withother canaliculi & vascular spaces

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Bone histology

CANCELLOUS BONETrabeculaeBone marrow

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Cancellous (spongy) bone

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Bone marrow

Bone marrow- a mixture ofadipose & hematopoietic cells

Platelet precursors: megakaryoblasts

RBC precursors: Erythroblasts / normoblasts Reticulocytes

WBC precursors:

myeloblasts Lymphoblasts Monoblasts

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Bone marrow

Platelet precursors:MegakaryoblastsMegakaryocytes

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Osteogenesis

Bone is formed from periosteal osteoblastsor from pre-existing connective tissue, mostcommonly hyaline cartilage

Endochondral ossificationIntramembranous ossification - periosteal bonegrowth

Hormonal requirements: parathormone,

growth hormone,Nutritional requirements:Vitamins C, D & minerals, esp CaProtein

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Endochondral ossification

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Endochondral ossificaton

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Calcium metabolism &

bone remodelingHormone controlParathormone secreted by the chief cells

of the parathyroid gland, it promotes release

of Calcium from bone, thus raising blood CalevelsCalcitonin secreted by the parafollicular

C cells of the thyroid gland, it promotesincorporation of Calcium into bone, thus

lowering blood Ca levelsOther hormones: GH, Thyroxine, Estrogen

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Bone remodeling

Nutritional requirements:Proteins

Vitamins: A, C, DMinerals: Ca, PO4

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Bone disorders

Osteoporosis poor mineralization ofbone due to deficiency of Calcium

Osteomalacia / Rickets softening or

demineralization of bone due to adeficiency of vitamin D in adults /children (bone deformities may

become permanent)

Osteoma benign bone growthOsteosarcoma malignant neoplasm ofbone

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Thats all !