Answer:
The term "bone collar" typically refers to a structure that forms during the development of long bones in vertebrates, like humans. The bone collar is a layer of bone that encircles the shaft or diaphysis of the developing long bone. It plays a crucial role in the formation of the bone and the growth process.
Here's how the bone collar is formed:
1. Mesenchymal Cells: In the early stages of bone development, mesenchymal cells differentiate into osteoblasts. Osteoblasts are the cells responsible for creating bone tissue.
2. Periosteum Formation: The osteoblasts gather around the outer surface of the developing cartilage model of the long bone. This gathering of osteoblasts forms a layer called the periosteum, which covers the outer surface of the bone.
3. Bone Matrix Secretion: Osteoblasts within the periosteum start to secrete bone matrix, which is primarily composed of collagen and minerals like calcium and phosphate. This secretion of bone matrix forms the initial bone collar.
4. Mineralization: The bone matrix becomes mineralized, which means that calcium and phosphate ions are deposited, turning the soft matrix into hard bone tissue.
5. Cartilage Breakdown: Inside the cartilage model of the long bone, chondrocytes (cartilage cells) continue to grow and divide, leading to the elongation of the bone. Meanwhile, osteoclasts begin to break down the central cartilage, allowing for the formation of the medullary cavity within the bone.
6. Ossification: The bone collar gradually expands, and further ossification processes convert the cartilage model into bone tissue, eventually replacing most of the cartilage with solid bone.
In summary, the bone collar is formed by osteoblasts within the periosteum surrounding the developing long bone. It represents the initial formation of bone tissue and plays a key role in the process of long bone development and growth.