The diaphysis is the long, tubular shaft of a long bone, primarily composed of compact bone. It provides structural support and strength, allowing the bone to withstand various forces during movement. The diaphysis contains the medullary cavity, which is filled with bone marrow, playing a crucial role in blood cell production. Surrounding the diaphysis is a layer of connective tissue called the periosteum, which helps in bone growth and repair. The diaphysis connects to the ends of the bone, known as the epiphyses, which are involved in joint movement and contain spongy bone and articular cartilage.