Cartilage is a connective tissue composed of cells (chondrocytes) and fibres (collagen or yellow elastic) embedded in a firm, gel-like matrix which is rich in a mucopolysaccharide. It is much more elastic than bone.
- Cartilage has no blood vessels or lymphatics. The nutrition of cells diffuses through the matrix.
- Cartilage has no nerves. It is, therefore, insensitive.
- Cartilage is surrounded by a fibrous membrane, called perichondrium, which is similar to periosteum in structure and function. The articular cartilage has no perichondrium, so that its regeneration after injury is inadequate.
- When cartilage calcifies, the chondrocystes die and the cartilage is replaced by bone.
Types of Cartilage
It is bluish white and translucent due to very fine collagen fibres. It distribution is most abundant, and has a tendency to calcify after 40 years of age. All cartilage bones are preformed in hyaline cartilage. Examples are embryonic cartilage, articular cartilage costal cartilages, tracheal and bronchial cartilages, and most of the cartilages of nose and larynx.
Hyaline cartilage has following roles in body
- Reduces Friction at Joints. By virtue of the smooth surface of hyaline cartilage, it provides a sliding area which reduces friction, thus facilitating bone movement.
- Movement: Hyaline cartilage joins bones firmly together in such a way that a certain amount of movement is still possible between them.
- Support: The c-shaped cartilagenous rings in the windpipes (trachea and bronchi) assist in keeping those tubes open.
- Growth: Hyaline cartilage is responsible for the longitudinal growth of bone in the neck regions of the long bones.
It is white and opaque due to abundance of dense collagen fibres. Wherever fibrous tissue is subjected to great pressure, it is replaced by fibrocartilage which is tough, strong and resilient. Exaples are intervertebral disc, intra-articular discs, menisci and labra. It lines certain bony grooves in which the tendons play.
- Shock Absorbers: The cartilage between the adjacent vertebrae absorbs the shocks that will otherwise damage and jar the bones while we run or walk.
- Support: Provides sturdiness without impeding movement.
- Movement: The white fibrocartilage forms a firm joint between bones but still allows for a reasonable degree of movement.
- Deepens Sockets: In articular cavities such as the ball-and-socket joints in the hip and shoulder regions white fibrocartilage deepens the sockets to make dislocation less possible.
It is made up of numerous cells and a rich network of yellow elastic fibres pervading the matrix, so that is more pliable. Example: cartilages in the external ear, auditory tube, and small cartilages at the inlet of larynx. It performs following functions.
- Maintain Shape: In the ear, for example, elastic cartilage helps to maintain the shape and flexibility of the organ.
- Support: Elastic cartilage also strengthens and supports these structures.