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
Cartilage Dentin
Bone
Enamel
Chondroblast Odontoblast
Osteoblast
Ameloblast
Osteoprogenitors
Scleroblast
collagen Fibroblast Myoblast Muscle cells
Mesenchymal cells
An Example: (chondrification)
• Mesenchymal cells retract processes Chondrification
• Congregate Center
• 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”
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”
An Example: (chondrification)
• Picture of cart.
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)
Compact lamellar bone
Membrane Bone
Compact lamellar
bone
Lamellar bone
Membrane bone