Cartilage Bone

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CartilageBone
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PRINCIPAL FUNCTIONS OF CARTILAGE

• supporting soft tissues
• covering the surfaces of bones forming the bone
  joints
• (shock absorber and sliding area)
• development and growth of long bones

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Chondrocytes Extracellular matrix

• GROUND SUBSTANCE
• Glicosaminoglicans (GAG)
• Proteoglicans
• hyaluronic acid

• FIBERS
• collagen fibers
• elastic fibers

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PERICHONDRIUM

• The capsule of connective tissue covering the
  cartilage
• outer layer - dense connective tissue
• collagen type I
• fibroblasts
• the source of nutrients for avascular
  cartilage
• inner layer
• chondroblasts - precursors of chondrocytes

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TYPES OF CARTILAGE

• Hyaline cartilage
• the most common form
• contains mainly collagen type II fibers
• Elastic cartilage
• many elastic fibers near the collagen type II
• more pliable than hyaline cartilage
• Fibrocartilage
• dense network type I collagen fibers
• present in regions subject to great
  mechanical stress

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HYALINE CARTILAGE

• articular surfaces of bones forming movable
  joints
• the walls of big respiratory passages
• larynx, trachea, bigger bronchi
• epiphyseal plates of long bones
• the cartilaginous parts of ribs
• covered by perichondrium
• (except articular cartilage)

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HYALINE CARTILAGE CHONDROCYTES

• develop from chondroblasts - cells present in the
  inner layer of the perichondrium
• at the periphery - elliptic shape
• farther in - become round , form isogenous groups
• isogenous group - develops by mitosis of single
  chondrocyte (5-8 cells in group)
• produce all components of extracellular matrix
• well developed RER, Golgi complex

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HYALINE CARTILAGE EXTRACELLULAR MATRIX

• collagen type II fibrils embedded in ground
  substance
• ground substance
• proteoglicans
• chondroitin sulfate, keratan sulfate
• long chains of hyaluronic acid
• chondronectin - glycoprotein providing adherence
  of collagen and chondrocytes
• water bound to the negative charges of
  glicosaminoglicans

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• Territorial matrix
• surrounds each chondrocyte of isogenous group
• rich in proteoglicans poor in collagen fibrils
• Interterritorial matrix
• occurs between isogenous groups
• numerous collagen type II fibrils
• Characteristics
• firm, resistant to compression

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ELASTIC CARTILAGE

• auricle of the ear
• the wall of external auditory canals
• auditory tubes (Eustachian tubes )
• epiglottis
• Presence of perichondrium

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ELASTIC CARTILAGE

• Chondrocytes
• similar to cells of hyaline cartilage
• smaller isogenous groups ( 2- 3 cells)
• Extracellular matrix
• abundant network of elastic fibers
• collagen type II fibrils
• ground substance the same components like in
  hyaline cartilage

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FIBROCARTILAGE

• annulus fibrosus of intervertebral disc
• symphysis pubis
• attachments of ligaments
• Great resistance to extention

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FIBROCARTILAGE

• Chondrocytes
• identical to cells of hyaline cartilage
• single or in groups
• groups - long raws of chondrocytes
• Extracellular matrix
• ground substance - less abundant
• numerous collagen type I fibers - bundles
• collagen bundles
• parallel to raws of cells
• visible in light microscope

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BONE

• Specific type of connective tissue with calcified
  extracellular substance
• Functions
• supporting soft tissues
• protection of important organs
• CNS in skull
• thoracic contents in chest
• reservoir of calcium

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OSTEOBLASTS

• form a layer which resembles the simple
  epithelium on the surface of bone
• surround themselves with matrix and become
  ostecytes
• basophilic cytoplasm
• abundant RER, well developed Golgi complex
• Functions
• synthesize the organic components of matrix
• responsible for calcification of bone matrix
• play certain role in bone resorption

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OSTEOCYTES

• develop from osteoblasts which surrounded
  themselves with matrix
• are located in matrix lacunae
• (one cell per lacuna)
• contact to each other by mean of cytoplasmic
  processes existing in canaliculi of matrix
• surrounded by thin layer of noncalcified matrix
• less RER, smaller Golgi complex condensed nuclear
  chromatin
• Function maintenance of the matrix

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OSTEOBLASTS OSTEOCYTES
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OSTEOCLASTS

• large, multinuclear cells
• derive from monocytes
  (belong to phagocyte system)
• ruffled border - surface facing bone ruffled
• clear zone - adhesion the cell to the matrix
• acidophilc cytoplasm
  abundant RER and Golgi complex numerous
  mitochondria and lisosomes
• Functions bone resorption
• bone growth and bone remodeling
• repair of fractures

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OSTEOCLASTS
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BONE EXTRACELLULAR MATRIX

• Organic components ( 30-35 of bone weight)
• collagen type I fibers ( 90)
• noncollagenous proteins
• osteonectin, osteocalcin, sialoproteins,
  phosphoproteins, proteolipids
• proteoglicans
• Inorganic components ( 70 of bone weight)
  calcium phosphate - hydroxyapatyte crystals

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Periosteum

• Layer of connective tissue covering the bone
• Outer layer - dense connective tissue
• fibroblasts
• numerous collagen fibers
• rich in blood vessels
  (source of vessels for bone)
• Inner layer
• osteoprogenitor cells
  (reservoir of osteoblasts)

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Endosteum

• Thin layer of connective tissue with
  osteoprogenitor cells
• Lines internal surfaces of the bone

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Types of bone

• IMMATURE BONE PRIMARY BONE
• woven bone
• MATURE BONE SECUNDARY BONE
• lamellar bone
• Compact bone
• Cancellous bone spongy bone

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SECUNDARY BONE MATURE BONE

• Present in adults
• Characteristics
• smaller number of osteocytes
• bone matrix
• abundant, well calcified
• arranged in lamellae
• regular arrangement of collagen fibers
• lamellae form osteons (Haversian systems)
• great resistance to mechanical forces

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SECUNDARY BONE MATURE BONE
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Endosteum

• Thin layer of connective tissue with
  osteoprogenitor cells
• Lines internal surfaces of the bone

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PRIMARY BONE IMMATURE BONE

• formed in embryo during bone formation
• develops in repair process after fracture
• replaced by mature bone
• irregular array of collagen fibrils in the
  organic part of matrix
• smaller calcification
• many osteocytes, little of bone matrix
• smaller mechanical resistance

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HISTOGENESIS

• Intramembranous ossification
• on the ground of mesenchymal tissue
• formation of flat bones
• e.g. bones of the skull
• Endochondral ossification
• on the ground of cartilaginous model of the bone
• formation of long bones

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INTRAMEMBRANOUS OSSIFICATION

• 1. penetration of blood vessels into mesenchymal
  tissue
• 2. mesenchymal cells differentiate into
  osteoblasts
• 3. formation of bone spicules

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ENDOCHONDRAL OSSIFICATION

• 1.
• formation of bone collar within an inner layer of
  perichondrium of the diaphysis
• (intramembranous ossification)

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ENDOCHONDRAL OSSIFICATION

• 2.
• hypertrophy of chondrocytes
• deposition of calcium salts in the cartilage
  matrix
• degeneration of chondrocytes

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ENDOCHONDRAL OSSIFICATION

• 3.
• penetration of osteogenic bud across bone collar
  into degenerated cartilage

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ENDOCHONDRAL OSSIFICATION

• 4.
• phagocytes resorb the cartilage
• osteoblasts start the production of bone matrix
  on the remnants of cartilage
• PRIMARY OSSIFICATION CENTER

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BONE GROWTHFLAT BONES

• 1. Formation of bone on the external surface
• osteoprogenitor cells of periosteum
  (intramembranous ossification)
• 2. Resorption of bone on the internal surface
• osteoclasts

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BONE GROWTH LONG BONES

• epiphyses - radial growth of cartilage cartilage
  is gradually replaced by bone
• the diaphysis increases in width by formation of
  bone by periosteum on the external surface
• diphyseal shaft grows in length as a result of
  the osteogenic activity of epiphyseal plate.

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