Using the structure of a long bone it is possible to identify a number of prominent features:

Diaphysis - the bone shaft. Epiphysis - each end of the bone (Epiphyses is the plural). Epiphyseal plate - the growth section - bones grow by lengthening at the ends. Periosteum - hard outer casing. Articular (Hyaline) Cartilage - cushions the ends (epiphyses) of the bone and protects them from wear. Yellow marrow - used to store fat in the bones. Red marrow - has blood production properties.

Bone Growth

The formation of bones, known as endochondral ossification, undergoes five main stages from the foetus to adulthood.

1. Formation of a bone collar around the shaft of the cartilage (pre-birth around 8 weeks).

Pre-birth bones are made of relatively soft cartilage. Osteoblasts (bone forming cells) appear in the centre of the cartilage diaphysis (the primary ossification centre) and begin to secrete osteoid against the hyaline cartilage shaft, encasing it on the outside in a bone collar.

2. The hyaline cartilage shaft develops cavities (pre-birth around 2-3 months).

As the bone collar forms on the outside of the diaphysis, the mature cartilage cells (chondrocytes) inside the shaft enlarge and the cartilage matrix calcifies. Nutrients cannot enter the calcified matrix and it begins to deteriorate causing cavities to open up and weaken the shaft. The deteriorating cartilage shaft is stabilized by the external bone collar.