Gross Anatomy of Bone

The anatomy of a bone is best exemplified by a long bone, such as the femur.

It comprises a long, central shaft — the diaphysis, that widens into the metaphysis at either side to meet the rounded ends called the epiphyses.

The epiphysis and metaphysis have a thin outer cortex of compact bone and an interior made of spongy or cancellous bone tissue.

Spongy bone is porous, with the spaces typically filled with red marrow.

In contrast, the diaphysis has a thick outer layer of compact bone surrounding the medullary cavity. This cavity, lined by the endosteum, is filled with lipid-rich yellow marrow in adults.

A double-layered membrane called the periosteum covers most of the length of a long bone except the epiphyseal ends.

Its outer membrane, composed of dense irregular connective tissue, provides attachment sites for ligaments and tendons.

The inner membrane houses osteogenic stem cells involved in bone growth and repair.

At the epiphysis, the articular cartilage covering the ends helps reduce friction and cushions joint movements.