In endochondral ossification, what invades the internal cavities to form spongy bone?

In endochondral ossification, what invades the internal cavities to form spongy bone?

• A. Periosteal bud
• B. Osteoclasts
• C. Nerve fibers
• D. Blood clots

Answer: (A)

In endochondral ossification, bone forms by replacing a cartilage model. A periosteal bud—consisting of blood vessels plus osteogenic cells from the periosteum—invades the internal cavities of the cartilage model. This invasion brings osteoblasts that lay down bone matrix, beginning the formation of spongy bone and establishing the primary ossification center in the diaphysis. As this process continues, cartilage at the center is resorbed to create the medullary (marrow) cavity. While osteoclasts participate in remodeling later, and while blood vessels are part of the invading bud, the key driver for making the spongy bone in the internal cavities is the periosteal bud.

In endochondral ossification, bone forms by replacing a cartilage model. A periosteal bud—consisting of blood vessels plus osteogenic cells from the periosteum—invades the internal cavities of the cartilage model. This invasion brings osteoblasts that lay down bone matrix, beginning the formation of spongy bone and establishing the primary ossification center in the diaphysis. As this process continues, cartilage at the center is resorbed to create the medullary (marrow) cavity. While osteoclasts participate in remodeling later, and while blood vessels are part of the invading bud, the key driver for making the spongy bone in the internal cavities is the periosteal bud.