Which process involves replacement of a cartilage model with bone?

Which process involves replacement of a cartilage model with bone?

• A. Intramembranous ossification
• B. Appositional growth
• C. Endochondral ossification
• D. Ossification center formation

Answer: (C)

Endochondral ossification. This process forms most bones by replacing a hyaline cartilage template with bone tissue. It begins with a cartilage model, then chondrocytes enlarge and the matrix calcifies, a periosteal bone collar forms, and blood vessels invade to bring osteoblasts that lay down bone, gradually replacing cartilage with bone. Longitudinal growth occurs at the growth plates as new cartilage is produced and subsequently ossified. In contrast, intramembranous ossification builds bone directly from mesenchyme without a cartilage stage, which is why it forms flat bones like those of the skull. Appositional growth increases bone diameter by adding new bone on the surface, not by replacing cartilage with bone. Ossification center formation is a stage within endochondral ossification, not the overall process name.

Endochondral ossification. This process forms most bones by replacing a hyaline cartilage template with bone tissue. It begins with a cartilage model, then chondrocytes enlarge and the matrix calcifies, a periosteal bone collar forms, and blood vessels invade to bring osteoblasts that lay down bone, gradually replacing cartilage with bone. Longitudinal growth occurs at the growth plates as new cartilage is produced and subsequently ossified. In contrast, intramembranous ossification builds bone directly from mesenchyme without a cartilage stage, which is why it forms flat bones like those of the skull. Appositional growth increases bone diameter by adding new bone on the surface, not by replacing cartilage with bone. Ossification center formation is a stage within endochondral ossification, not the overall process name.