endoszteum

Endosteum is a thin cellular membrane that lines the inner surfaces of bones, including the medullary (marrow) cavity, the trabeculae of cancellous bone, and the canals within compact bone. It forms the inner counterpart to the outer periosteum and is typically much thinner and less conspicuous.

The endosteum consists of a delicate layer of osteogenic cells resting on a basement membrane, with only a sparse connective tissue component. Its cellular population includes osteoprogenitor cells that can differentiate into osteoblasts, as well as mature osteoblasts that may line internal bone surfaces during remodeling. Osteoclast precursors are present as part of the remodeling milieu, enabling coordinated bone resorption and formation at internal surfaces.

Location and structure give the endosteum a key role in bone growth, repair, and remodeling. By supplying osteogenic cells, it supports the formation of new bone tissue in response to stress or injury. During fracture healing, endosteal progenitors contribute to forming new bone in the callus and re-establishing internal bone architecture. The endosteum also participates in mineral homeostasis by regulating the exchange of calcium and other minerals between bone and the marrow environment.

In summary, the endosteum is a minor but important inner lining of bone that provides progenitor cells for bone formation, participates in remodeling, and helps maintain skeletal mineral balance. It operates in concert with the periosteum and the coordinated activity of osteoblasts and osteoclasts to sustain bone health.