Where do the osteoblasts come from after a fracture has occurred?

The osteoblasts that help repair a fracture originate from two primary sources:

1. Local Osteoprogenitor Cells: Within the bone tissue, there are specialized cells called osteoprogenitor cells. These cells are essentially immature bone-forming cells that reside near the surfaces of existing bone tissue. When a fracture occurs, the damaged area releases signals that stimulate the osteoprogenitor cells to become active. They differentiate into osteoblasts and start producing new bone matrix to fill the fracture gap.

2. Bone Marrow Stromal Cells: The bone marrow, which occupies the central cavity of bones, contains a population of multipotent stromal cells. These stromal cells have the ability to differentiate into various cell types, including osteoblasts. Upon the occurrence of a fracture, certain factors and growth signals released at the injury site promote the differentiation of stromal cells into osteoblasts.

These osteoblasts derived from both local osteoprogenitor cells and bone marrow stromal cells play a critical role in the process of fracture healing, where they synthesize and deposit new bone tissue to bridge the fractured bone ends.