Overview
This lecture examines the microscopic structure and developmental zones of endochondral bone formation, focusing on the transitions from cartilage to bone.
Histological Zones of Endochondral Bone Development
- The uppermost section is called the zone of resting cartilage, where cartilage cells are small and inactive.
- Below this is the zone of proliferation, where chondrocytes (cartilage cells) actively divide and begin to organize into columns.
- Beneath the proliferative zone lies the zone of hypertrophy, where chondrocytes enlarge and the lacunae (spaces) become bigger.
- The zone of calcification follows, marking the transition from cartilage to bone as minerals are deposited and cartilage cells die.
- The deepest area is ossified bone, where the cartilage is completely replaced by mature bone tissue.
Key Terms & Definitions
- Chondrocyte â a cartilage cell involved in bone development.
- Lacuna (plural: lacunae) â small cavities in cartilage or bone that house cells.
- Zone of Resting Cartilage â region with inactive chondrocytes at the epiphyseal plate.
- Zone of Proliferation â area where chondrocytes divide rapidly, forming columns.
- Zone of Hypertrophy â region where chondrocytes enlarge and spaces widen.
- Zone of Calcification â transitional area where cartilage becomes mineralized and starts to turn into bone.
- Ossified Bone â fully formed bone tissue, replacing the cartilage matrix.
Action Items / Next Steps
- Review histology slides to identify and label the four zones of endochondral bone development.
- Prepare to discuss the functional significance of each zone in class.