Bone development phases

phase I- cells involved

• mesenchymal 

• osteoblasts

• chondrocytes

phase I- summary

• Mesenchyme cells become osteoblasts

• Perichondrium becomes periosteum

• Osteoblasts secrete osteoid, create bone collar

• Chondrocytes hypertrophy and become primary ossification center

phase II- cells involved

• chondrocytes

phase II- summary

• Chondrocytes ossify

• Chondrocytes die and matrix dissolves

• New cavities are formed

phase III- cells involved

• osteoclasts

• osteoprogenitor

• osetoblasts

phase III- summary

• periosteal bud appears

• osteoclasts erode cartilage matrix

• osteoprogenitor cells become osteoblasts; spongy bone starts to form

phase IV- cells involved

• osteoclasts

phase IV- summary

• osteoclasts break down new spongy bone (open cavities)

• secondary ossification centers form

phase V- summary

• secondary centers mimic the cycle of the primary

• epiphyseal plate follows patter for elongation growth