VMBO Year 3 · Support and movement · Section 5.2

Cartilage and bone tissue

How do cartilage and bone differ?

Both cartilage and bone tissue support the body. Cartilage is firm but flexible. It occurs in places such as the nose, outer ears and joint surfaces. Cartilage cells often lie in small groups within an extracellular matrix. The matrix's composition gives different types of cartilage their flexibility and resistance to pressure.

Why are bones hard but slightly flexible?

Bone tissue is harder than cartilage. In compact bone, many cells lie in rings around small canals containing blood vessels. Tiny channels connect the cells. Two important components of the matrix are calcium salts and collagen. Mineral salts provide hardness and resistance to compression; collagen fibres provide tensile strength and some flexibility. Together they make bone strong without being as brittle as mineral alone.

How does the skeleton change during life?

Much of the developing skeleton begins as cartilage which is gradually replaced by bone. Children's bones tend to be more flexible and contain growth regions of cartilage. Throughout life, bone is continually broken down and rebuilt. With ageing, bone density and quality may decrease, making fractures more likely. Ageing is not simply a continuous increase in calcium: mineral loss can also be important.

A classroom demonstration

In a supervised experiment, acid removes much of a bone's mineral content, leaving it more flexible. Strong heating destroys its organic material, including collagen, leaving a brittle mineral structure. These demonstrations show how both components contribute to bone strength.