Cartilage

Cartilage is a member of the supporting connective tissue group, characterised by a matrix that is hard yet, unlike bone, still somewhat pliable. It forms the entire endoskeleton of cartilaginous fishes such as the shark, and is otherwise widely distributed throughout vertebrate animals wherever a flexible support is needed.

In cartilage, an abundant matrix is bounded at its edge by a sheath of collagenous fibres called the perichondrium. The matrix itself is called chondrin. Immediately beneath the perichondrium lie immature, cartilage-forming cells called chondroblasts; as these mature they convert into chondrocytes, which come to lie scattered through the matrix, each enclosed within a small fluid-filled space called a lacuna (each lacuna typically holding 2 to 8 chondrocytes).

Based on what the matrix additionally contains, four types of cartilage are recognised:

Hyaline cartilage (hyaline = glass-like): perichondrium is present; the matrix is bluish-white and gel-like, containing very fine collagen fibres along with the chondrocytes. It is elastic and compressible, making it a good shock absorber that also provides flexibility and reduces friction at joints. It is found at the ends of long bones, and in the epiglottis, trachea, ribs, larynx and hyoid.

Elastic cartilage: perichondrium is present; the matrix contains elastic fibres, and chondrocytes are comparatively few in number. It gives support and helps maintain the shape of the body part it supports. It is found in the ear lobe (pinna) and the tip of the nose. …