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BONE

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DEFINATION OF BONE

Bone is a highly vascular, rigid form of specialized scleral connective tissue in which the extracellular matrix is impregnated with inorganic salts which provide hardness, organic material like cells.

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Comparison of bone with ordinary connective tissue

Chracteristics

Ordinary connective tissue

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Cartilage

Bone

Matrix

Glycosaminoglycans (viscous)

Gel like consistancy (more water)

Rigid & hard impregnation of calcium salts

Cells

Blood cells

Fibroblast

Chondrocyte

Osteocyte

Osteoblast

Osteoclast

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Structure of bones:

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Bone membranes:

  • Periosteum
  • Endosteum

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Bone membranes: periosteum

Dense connective tissue

Functions of periosteum:

  • Provides attachment
  • Nutrition
  • Bone growth & repair
  • Fibrous layer of periosteum act as limiting membrane

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BONE MEMBRANES: ENDOSTEUM

Vascular

Loose connective tissue

Functions of endosteum:

  • Bone growth & repair

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Bone composition as a specialized connective tissue:

  • Cells
  • Fibres = collagen fibres
  • Ground substance = proteoglycans
  • Inorganic components = calcium salts

(provides hardness and rigidity to the bone)

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Bone compositon as a specialized connective tissue :-

  • Cells:
  • Osteoprogenitor cells
  • Osteoblast
  • Osteocyte
  • Osteoclast

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Osteoprogenitor cells - stem cell .

Site where osteoprogenitor cells are present:

  • Site of bone formation in fetus
  • In adult, osteogenic layer of periosteum and endosteum .
  • At the site of bone repair.

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Osteoblasts = bone forming cells

Site where osteoblasts are present:

  • Site where new bone formation occure.

Functions:

  • Laying down organic matrix (Secrete matrix = collagen fibre & ground substance.)
  • Control the bone resorption

Applied: Osteoma & osteosarcoma

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Osteocytes = cells of mature bone (bone maintainer)

Site where osteocytes are present:

  • Embedded in bone matrix surrounded by lacuna and canaliculi

Functions:

  • Maintain the integrity of lacunae & canaliculi
  • Role in removal & deposition of matrix & calcium

FILAPODIA

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Osteoclasts = bone removing cells

(bone destroyer)

Site where osteoclasts are present:

  • On bone surface at site of bone resorption

HOWSHIP’S LACUNAE (RESORPTION BAY)

RUFFELED BORDER

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BONE COMPOSITON AS A SPECIALIZED CONNECTIVE TISSUE:

  • FIBRES :-
  • Type - I collagen fibres (osteoid collagen ) = embedded in ground substance.
  • Synthesized by - osteoblasts.

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  • Flexibility of bone , provide tensile strength to the bone.

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  • Collagen fiber within the lamella oriented parallel to each other but fiber in one lamella are at right angle to adjucent lamella.

BONE MATRIX :- 1) ORGANIC.

2) INORGANIC.

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  • GROUND SUBSTANCE:
  • Small amount of amorphous substance rich in proteoglycans ,

short core of protein & fews chains of glycosaminoglycans

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  • glycosaminoglycans = hyaluronic acid,

chondroitin sulfate , keratan sulfates.

  • Hydroxyapetite crystal & collagen fiber are embedded in acidic ground substance.

Osteoid:

The mixture of organic ground substance and collagen fibers before it is mineralized.

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BONE MATRIX :- INORGANIC MATRIX .

Crystal of calcium phosphate , calcium carbonate ,

calcium fluoride , citrate , magnessium , & sodium .

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Rod like crystal arranged along the length of

Collagen fiber.

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A layer of water & ions surround each crystal.

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Hardness of bone , provide compressive strength

to the bone.

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COMPACT BONE:

Diaphysis ( shaft ) of long bone ,

Thin layer on external surface of all other bone which

Core is made up of spongy bone , short , flat ,irregular bone.

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No space is visible on naked eye examination so called ….

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Its outer surface is covered by - Periosteum

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Its inner surface is covered by - Endosteum

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STRUCTURE OF COMPACT BONE:

Consists of three systems (sets) of bony lamellae

Arranged in an orderly manner:

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          • Circumferential system:
              • Outer (periosteal)
              • Inner (endosteal)

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          • Haversian system / osteon :-
              • Concentric lamellae.

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          • Interstitial system

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STRUCTURE OF COMPACT BONE :-

  • Circumferential system:
      • Outer (periosteal)
      • Inner (endosteal)

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  • Haversian system of lamellae / osteon

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STRUCTURE OF COMPACT BONE:

  • Haversian system / osteon

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STRUCTURE OF COMPACT BONE:

  • Haversian system / osteon

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STRUCTURE OF COMPACT BONE:

  • Interstitial system

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Compact bone, Dried : An Osteon (T.S.)

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Compact bone, Dried (T.S.)

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Compact bone, Dried (L.S.)

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STRUCTURE OF SPONGY / CANCELLOUS BONE:

Epiphysis of long bone , short , flat , irregular bones.

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Thin rim around marrow cavity of diaphysis of long bone.

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Differentiating characteristics from compact bone:

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  • Presence of bony trabeculae separated by marrow space containing bone marrow.

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  • Absence of haversian system.

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  • Osteocytes are seen embedded in the matrix of the trabeculae

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Cancellous bone : (T.S.) , decalcified

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Cancellous bone :-

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Formation of bone:

  • Ossification:
  • Calcification:
  • Decalcification:
  • Calcination:

Methods of bone formation:

  • Intramembranous ossification
  • Endochondral ossification

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FORMATION OF BONE:

  • INTRAMEMBRANOUS OSSIFICATION

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FORMATION OF BONE:

  • ENDOCHONDRAL OSSIFICATION

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FORMATION OF BONE:

  • ENDOCHONDRAL OSSIFICATION

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FORMATION OF BONE:

  • ENDOCHONDRAL OSSIFICATION