Lecture Notes: Bone Tissue Formation and Growth

Mechanisms of Bone Formation

Endochondral Ossification

• Begins with hyaline cartilage
• Cartilage is replaced by bone tissue after it dies

Intramembranous Ossification

• Starts with a mesenchyme sheet (fibrous connective tissue)
• Mesenchymal cells transform into osteoblasts
• Osteoblasts secrete matrix, forming spongy bone
• Primarily occurs in the fetus

Bone Growth in Children and Adolescents

• Bones continue to grow in length and thickness
• Growth mechanisms:
  • Reference to intramembranous and endochondral ossification
  • Growth in length and thickness
  • Comparison of bone growth and remodeling

Endochondral Ossification and Bone Growth

• Cartilage template (hyaline cartilage) almost replaced by bone
• Formation of bone shaft and nutrient artery
• Secondary ossification centers in epiphysis
• Thin layer of articular cartilage remains
• Epiphyseal plate with living chondrocytes allows for growth

Bone Growth in Length

• Occurs at the epiphyseal plate where cartilage proliferates
• Chondrocytes grow and cartilage is replaced by bone tissue

Bone Growth in Width

• Osteoblasts under the periosteum secrete matrix
• Bone increases in width due to mechanical stresses
• Electrical signals from muscles help maintain bone health

Bone Remodeling

• Continuous turnover of bone tissue
• Old bone broken down by osteoclasts, replaced by osteoblasts
• Responds to hormonal and mechanical changes

Osteoclast and Osteoblast Activity

• Osteoclasts dissolve bone tissue
• Osteoblasts lay down new matrix
• Balanced activity keeps bones healthy

Imbalances in Activity

• Excessive breakdown leads to osteoporosis
• Excessive buildup may lead to Paget's disease

Mechanical Stress and Bone Remodeling

• Example: Weightlifting increases bone size due to muscle stress
• Astronauts experience bone thinning due to lack of gravity

Discussion Topic

• How x-rays of the femur can indicate if someone has reached full height