Bone Growth & Development

• Bone Development

  Formation of bone = ossification or osteogenesis
• Bone Development

  • Starts with mesenchyme tissue (connective tissue found in embryo)
  • Undifferentiated stem cells
  • Loosely organized
  • During development, gives rise to nearly every organ in developing embryo
• Types/mechanisms of bone development

  • Intramembranous ossification
  • Endochondral ossification
• Intramembranous Ossification


  1. Mesenchyme bone

  2. Spongy bone forms first

  3. Mesenchymal stem cells differentiate into osteoblasts secrete matrix

  4. Osteoblasts become osteocytes as matrix calcifies (calcium phosphate deposited)

  5. Periosteum forms second

  6. Mesenchyme tissue condenses becomes periosteum

  7. Compact bone forms last

  8. Osteoblasts lay down layers of bone deep to periosteum
• Endochondral Ossification


  1. Mesenchyme cartilage bone

  2. First, cartilage blueprint created

  3. Mesenchymal stem cells differentiate into chondroblasts chondrocytes

  4. Next, primary ossification center created (middle of diaphysis)

  5. Chondrocytes die, matrix calcifies

  6. Mesenchymal stem cells osteogenic stem cells osteoblasts osteocytes (as matrix calcifies)

  7. Next, primary marrow cavity created

  8. Blood vessels bring osteoclasts dissolves matrix to create cavity

  9. Next, secondary ossification center & secondary marrow cavity created in epiphyses

  10. At birth, cartilage remains at ends of bones

  11. Spongy bone replaces cartilage in epiphyses

  12. Children retain hyaline cartilage in epiphysial plate to allow for bone lengthening

  13. Adults – no more internal cartilage (only articular cartilage)
• Bone Growth - Length

  Interstitial growth at epiphysial plate via endochondral ossification
• Bone Growth - Width

  Appositional growth just below periosteum via intramembranous ossification
• Interstitial Growth


  1. New cartilage produced on epiphysial side

  2. New bone deposited on diaphysis side (conversion from cartilage bone)
• Appositional Growth


  1. Inner layer of periosteum: osteoblasts create new bone tissue

  2. Creates circumferential lamellae increase in bone diameter
• Bone Remodeling

  1. Absorption & replacement of bone

  2. Collaboration between osteoblasts and osteoclasts

  3. Occurs throughout adult life

  4. Entire skeleton replaced ~every 10 yrs

  5. Repairs microfractures

  6. Releases minerals into blood

  7. Reshapes bones in response to use and disuse
• Wolff's Law


  A bone grows or remodels in response to mechanical forces or stress placed upon it