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 cells Scleroblast Osteoblast ChondroblastOdontoblast Ameloblast Bone CartilageDentin 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)

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 Bone Compact lamellar bone

Compact lamellar bone

Lamellar bone

Membrane bone