Year 1 · Support and movement · Section 4.2

Bone structure

Bone and cartilage

Bone contains calcium salts and collagen. Calcium salts make bone hard, while collagen provides some flexibility and resistance to pulling forces. Together they make bone strong without being completely brittle.

The skeleton contains two important tissues:

• Cartilage: Cells often occur in small groups within a flexible extracellular matrix containing collagen. Cartilage is found in the nose, outer ears, between ribs and the sternum, and in the discs between vertebrae.
• Bone tissue: In compact bone, cells occur in layers around small canals containing blood vessels. The matrix contains calcium salts and collagen, making it hard but slightly flexible.

Changes during growth and ageing

Much of the developing skeleton begins as cartilage, which is gradually replaced by bone. A baby's skull bones are not fully joined. Soft spaces between them, called fontanelles, contain connective tissue.

Children's bones are generally more flexible than adults' bones. As people age, changes in bone structure and quality can make bones more fragile. Ageing does not simply mean that bones gain more calcium; loss of bone mineral can also increase fracture risk.

The largest fontanelle usually closes during the second year of life, often around 18 months. The joints between the skull bones remain visible as sutures.