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Bone and Bone Precursors
The skeleton
• Mineralized connective tissue
• Ligaments– connecting bone to bone– holds some organs in place
• Tendons– Extension of muscle and bone
Flow chart for histogenesis of skeletal tissues
Mesenchymal cells
Fibroblastcollagen Myoblast Muscle cellsScleroblast
OsteoblastChondroblast Odontoblast
Ameloblast
BoneCartilage Dentin
Enamel
Osteoprogenitors
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
An Example: (chondrification)
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”
• Picture of cart.
An Example: (chondrification)
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
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
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)
Membrane BoneCompact lamellar bone
Compact lamellarbone
Lamellar bone
Membrane bone