Gross Anatomy of Long Bone

The gross anatomy of a long bone

Long bone consists of several distinct parts that work together to support the body and enable movement. The central shaft of the bone is called the diaphysis, which is mainly composed of strong compact bone that provides strength and shape. Inside the diaphysis is the medullary cavity, a hollow space filled with yellow bone marrow that stores fat. At each end of the bone are the epiphyses, which are the rounded ends made mostly of spongy bone containing red bone marrow, responsible for producing blood cells. The epiphyses are covered with articular cartilage, a smooth tissue that reduces friction and absorbs shock at the joints. Between the diaphysis and epiphyses lies the metaphysis, which includes the epiphyseal plate (growth plate) in growing bones. In adults, this becomes the epiphyseal line, indicating where growth has stopped. Surrounding the outer surface of the bone is the periosteum, a tough, fibrous membrane rich in blood vessels and nerves, which helps in bone growth, repair, and provides attachment for muscles. Lining the inner surface of the medullary cavity is the endosteum, a thin layer that also contains bone-forming cells. Together, these parts make the long bone a strong, living structure that plays a key role in movement, support, and the production of blood cells.