L4.4.2: Bone Formation

• Ossification (Osteogenesis)

  Is the process of bone formation. Occurs on hyaline cartilage models or fibrous membranes. Has 2 pathways:

  • Endochondral ossification
  • Intramembranous ossification
• ENDOCHONDRAL OSSIFICATION

  ● Hyaline cartilage is being converted into bone by secretion of bony matrix
• INTRAMEMBRANOUS OSSIFICATION

  ● Mesenchymal cells are embryonic cells that undergo differentiation to become bones
• Long bone growth involves two major phases:

  ○ Osteoblasts (bone-forming cells) cover hyaline cartilage model with bone matrix

  ○ In a fetus, the enclosed cartilage is digested away, opening up a medullary cavity
• By birth, most cartilage is converted to bone except for two regions in a long bone:

  ○ Articular Cartilages - Epiphyseal of long bone that prevents damage caused by friction

  ○ Epiphyseal Plates - Involved in the increase in the length of bones
• ● New cartilage is formed continuously on external face of these two cartilages

  ● Old cartilage is broken down and replaced by bony matrix