What is active tissue in bone?

The active tissue in bone is called the endosteum. The endosteum is a thin membrane that lines the inner surface of the bone cortex and serves as a source of new bone formation. It consists of a monolayer of osteoblasts and a layer of bone lining cells. Osteoblasts are responsible for the synthesis and deposition of new bone matrix, while the bone lining cells are responsible for lining the surface of the bone and regulating bone resorption. The endosteum is also involved in the regulation of hematopoiesis and the maintenance of the bone marrow microenvironment.