The central cavity of bone shafts where red bone marrow and/or yellow bone marrow (fatty tissue) is stored. This space runs the length of the diaphysis, the main midsection of a long bone. It is lined by a thin layer of cells called the endosteum and plays a crucial role in hematopoiesis (blood cell formation) in younger individuals when it contains red marrow. As an individual ages, the red marrow is often replaced by yellow marrow, primarily composed of fat cells.
The presence of this internal space significantly reduces the overall weight of bone without compromising its strength. This weight reduction is essential for efficient movement. Furthermore, the marrow housed within this space serves vital functions, including the production of blood cells and the storage of energy reserves. Historically, the study of this anatomical feature has been fundamental to understanding bone physiology and various bone-related disorders.
