Bone and Bone Precursors

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Bone and Bone Precursors
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The skeleton

• Mineralized connective tissue
• Ligaments
• connecting bone to bone
• holds some organs in place
• Tendons
• Extension of muscle and bone

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Flow chart for histogenesis of skeletal tissues
Cartilage
Dentin
Bone
Enamel
Chondroblast
Odontoblast
Osteoblast
Ameloblast
Osteoprogenitors
Scleroblast
Fibroblast
collagen
Muscle cells
Myoblast
Mesenchymal cells
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An Example (chondrification)

• Mesenchymal cells retract processes
• Congregate
• These cells become Chondroblasts
• Secrete matrix about themselves
• Form lacunae
• Become Chondrocytes
• Chondroblasts in middle
• 2-4 cells within a lacunae still
  chondroblasts
• Result from a single cell mitotically dividing.
• Secrete matrix push away from each other
  chondrocytes
• interstitial growth

Chondrification Center
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An Example (chondrification)
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An Example (chondrification)

• Mesenchyme cells on periphery
• Differentiate to form fibroblasts that produce
• Dense irregular collagenous connective tissue
  (perichondrium)
• Responsible for growth and maintenance of cart.
• Perichondrium - two layers
• Outer fibrous layer
• Inner cellular layer mainly chondrogenic cells
• Mitosis to form chondroblasts produce matrix
• appositional growth

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An Example (chondrification)

• Picture of cart.

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Bone

• Specialized connective tissue of
• calcified bone matrix
• 3 cell types
• Osteocytes, in lacunae
• osteoblasts make new matrix and maintain old
  matrix
• osteoclasts multinucleated giant cells
  phagocytose bone matrix in remodeling bone
• Viewed as ground bone sections or decalcified and
  embedded paraffin sections
• Endosteum and periosteum

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Bone Functions

• Support soft tissues
• Locomotion
• Protect vital organs (skull, ribs, vertebrae)
• Bone marrow (hematopoiesis)
• Process of differentiation of various cells from
  stem cells
• Reservoir of calcium and phosphate

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Bone Matrix

• Synthesized and maintained by osteoblasts and
  osteocytes
• 50 of dry wgt is inorganic calcium and
  phosphate
• Hydroxyapatite crystals
• Organic part is 95 type I collagen with
  amorphous ground substance (glycoproteins)

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Compact lamellar bone
Membrane Bone
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Compact lamellar bone
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Lamellar bone
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Membrane bone