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 contains blood vessels and nerves. The diaphysis is essential for the overall function of long bones, such as those found in the arms and legs, contributing to the body's mobility and stability.