Structure of a typical long bone

Structure of a typical long bone

A typical long bone (Figure 9.12) is built from a diaphysis, two epiphyses (singular epiphysis) and surrounding membranes. The tubular diaphysis (shaft) forms the bone's long axis; it is a thick collar of dense compact bone surrounding a hollow central medullary (marrow) cavity. The epiphyses are the bone's rounded ends: their exterior is compact bone, but their interior is spongy bone containing red marrow. The transition zone where the diaphysis meets each epiphysis is the metaphysis, and in a growing bone this is where the epiphyseal (growth) plate is located.

The entire external bone surface (except at joint surfaces) is wrapped in a double-layered membrane, the periosteum: its outer layer is dense, irregular connective tissue, while its inner, "osteogenic" layer contains osteoblasts (bone-forming cells) that secrete new bone matrix, osteoclasts (bone-resorbing cells), and primitive osteogenic stem cells that give rise to fresh osteoblasts. The periosteum is richly supplied with nerves, lymphatic vessels and blood vessels, which is part of why a periosteal injury (as in a fracture) is so painful. Internally, bone surfaces are lined by a thinner connective-tissue membrane, the endosteum, which covers the spongy …