The arrangement of compact and spongy tissue in long bone accounts for its strength. Long bones contain sites of growth and reshaping and structures associated with joints. The parts of a long bone include the following:

Diaphysis- The diaphysis is the long shaft of the bone. It is composed primarily of compact bone and therefore provides considerable strength.

Epiphysis- The enlarged ends of the long bone are the epiphyses. The epiphyses of a bone articulates, or meets, with a second bone at a joint. Each epiphysis consists of a thin layer of compact bone overlying spongy bone. The epiphyses are covered by cartilage.

Epiphyseal disc or plate- A growing bone contains a band of cartilage located at the ends of long bones, between the epiphyisis and the diaphysis. This band of cartilage is the epiphyseal plate. It is here that longitudinal bone growth occurs.

Medullary cavity- The medullary cavity is the hollow center of the diaphysis. In infancy, the cavity is filled with red bone marrow for blood cell production. In the adult, the medullar cavity is filled with yellow bone marrow and functions as a storage site for fat; at this stage it is not associated with blood cell production. The inside of the medullary cavity is lined with connective tissue called the endosteum.

Periosteum- The periosteum is a tough fibrous connective tissue membrane that covers the outside of the diaphysis. It is anchored firmly to the outside of the bone on all surfaces except the articular cartiglage. The periosteum protects the bone, serves as a point of attachment for muscle, and contains blood vessels that nourish the underlying bone. Because the periosteum carries the blood supply to the underlying bone, any injury to this structure has serious consequences to the health of the bone. Like any other organ the loss of blood supply can cause its death.

Articular cartilage- The articular cartilage is found on the outer surface of the epiphysis. It forms a smooth, shiny surface that decreases friction within a joint. Because a joint is also called an articulation, this cartilage is called articular cartilage.