Bone Growth and Remodeling

Long Bone Growth

• Endochondral Ossification
  • Process by which long bones grow in length.
  • Involves the transformation of hyaline cartilage into bone.
  • Steps of endochondral ossification:
    1. Formation of Bone Collar
       • Osteoblasts secrete osteoid around the diaphysis.
    2. Cartilage Degradation
       • Calcification starts, leading to cartilage degradation.
    3. Primary Ossification Center Development
       • Located at the center of the diaphysis.
       • Formation of spongy bone as osteoclasts degrade calcified cartilage.
    4. Medullary Cavity Formation
       • Blood vessels enter; secondary ossification centers appear in epiphyses.
    5. Bone Maturation
       • Hyaline cartilage remains in growth plate (epiphyseal plate) until adulthood.
       • Eventually, ossifies around age 20, leaving articular cartilage at bone ends.

Intramembranous Ossification

• Occurs in bones of the skull.
• Process
  • Begins with a fibrous connective tissue membrane.
  • Osteoblasts secrete osteoid, forming ossification centers.
  • Growth of spongy bone from center outward, surrounded by compact bone.

Bone Remodeling

• Continues after bones stop growing in length.
• Appositional Growth
  • Bones can grow horizontally, widening or narrowing as needed.
• Wolff's Law
  • Bone grows in response to demands placed on it.
  • Example: Long bones thickest midway due to bending stress.
  • Curved bones thickest where they likely to buckle.
  • Implications for bone density changes based on activity levels.